The Immediate Supply of Information (SII) is the system for maintaining VAT registration books in near real time through the AEAT electronic office. Since its implementation in 2017 for large taxpayers, it has steadily become the benchmark for tax control and, in parallel, has forced thousands of accounting firms and companies to review their accounting software. Contasol, the professional accounting solution from TeamSystem España, has long included a native SII module, but configuring it correctly — and keeping it operational every time the AEAT updates its schemas — requires knowing exactly what you are doing.
In this article we explain how the Contasol integration with the SII works, which registration books it affects, what the actual submission deadlines are, which errors appear most frequently, and when it makes sense to bring in a specialist to set everything up correctly from the start.
What is the SII and who is required to use it
The SII regulates the electronic maintenance of VAT registration books through the near-immediate supply of information to the AEAT. It is governed by Royal Decree 596/2016 and the successive ministerial orders that have updated the XML schemas of the records. It is mandatory for VAT taxpayers whose volume of transactions exceeded 6 million euros in the previous year, although those who do not reach that threshold may also opt in voluntarily.
The books maintained through the SII are four:
- Register of issued invoices.
- Register of received invoices.
- Register of investment goods.
- Register of certain intra-community transactions.
Each record must be submitted within a maximum of four business days from the date of issue or accounting entry of the invoice, excluding Saturdays, Sundays and national public holidays. For transactions with periodic settlement, deadlines may vary slightly; the AEAT publishes the updated official calendar on its electronic office.
Contasol and the SII: what the native module includes
Contasol offers, in its Standard, Elite and Cloud versions, an SII module (contracted separately as an add-on) that connects directly to the AEAT web services using a digital certificate or the Cl@ve system. The basic workflow is as follows:
- The accountant records invoices in Contasol using the standard journal entry coding.
- The SII module automatically generates XML files with the structure required by the AEAT.
- Submission takes place from within Contasol itself, without needing to access the electronic office separately.
- The AEAT response (accepted, accepted with errors, rejected) is stored in the submission history for review and, where necessary, correction.
The Contasol SII module is compatible with the main invoice types: simplified, corrective, intra-community transactions, reverse charge, property rental transactions and special regimes such as the RECC (Cash Accounting Special Regime). This broad coverage is one of the reasons why many mid-sized accounting firms have adopted it as their central tool.
Key differences between the SII and Verifactu: they are not the same thing
One of the most common mistakes we encounter when speaking with accounting firms is confusing the SII with Verifactu. They are two distinct obligations with different purposes:
| Feature | SII | Verifactu |
|---|---|---|
| What is submitted | VAT registration book records (issued/received invoices) | Billing records at the moment of issue |
| Who is required | Taxpayers with >6 M€ annual turnover | All legal entities from 1 Jan 2027; self-employed from 1 Jul 2027 |
| Legal basis | RD 596/2016 and successive orders | RD 1007/2023 (Verifactu Regulation) |
| Invoicing software | Does not apply directly to invoicing software | Requires the invoice-issuing software to comply (manufacturer's responsible declaration) |
| Mutual compatibility | SII and Verifactu are mutually exclusive: SII taxpayers are exempt from Verifactu | |
This last point is important: if your company is already in the SII, you do not need to worry about Verifactu for your accounting software. But if your accounting clients do not exceed the SII threshold, you will need to ensure that their invoicing software complies with Verifactu before the deadlines (legal entities: 1 January 2027; self-employed: 1 July 2027).
Regarding the Verifactu compliance mechanism: there is no AEAT «approval» or official list of certified software. The mechanism established by RD 1007/2023 is the manufacturer's responsible declaration. Contasol, which includes the SII module for its obligated users, does not fall within the scope of Verifactu for those same users.
Configuring Contasol for the SII: critical steps
Getting the SII up and running in Contasol is not simply flipping a switch. There are a number of steps that, if skipped or done in the wrong order, generate validation errors at the AEAT that require mass resubmissions. The most important ones:
1. Digital certificate and AEAT permissions
Submitting SII records requires a digital certificate of the legal entity or an authorised representative. Before configuring Contasol, verify that the certificate is valid, installed in the operating system certificate store, and that the user has the correct permissions on the electronic office. An expired certificate or one installed under the wrong user profile is the number one cause of rejections in the first submissions.
2. Correct coding of invoice types
The AEAT defines specific invoice types in its XML schemas (F1, F2, F3, R1, R2, R3, R4, R5 for issued; F1, F2, F3, F4, F5, LC for received). Contasol maps these types according to the chart of accounts configuration and the VAT types used. A frequent mistake is incorrectly configured journal entries for corrective invoices or reverse-charge transactions, which generates rejections of the type «invoice type inconsistent with record data».
3. Managing submission deadlines
The four business-day deadline runs from the date of issue (issued invoices) or from the date of accounting entry (received invoices, with the additional limit of the settlement period). Contasol allows you to configure submission deadline alerts so that the accounting firm does not miss the deadline. In practice, most accounting firms set up daily batch submissions, which is perfectly valid provided the maximum deadline is respected.
4. Handling error records
When the AEAT returns a record with status «AcceptedWithErrors» or «Incorrect», the process does not end there. You must review the error code, correct the journal entry in Contasol and resubmit the corrected record. Contasol maintains a submission history showing the status of each record, which makes this task easier, but requires someone to review it regularly. Leaving records in an error state without resolving them can lead to AEAT enquiries.
Common use cases in accounting firms
At Summum Sistemas — Official TeamSystem Partner in Castilla y León and the Canary Islands — we have configured the Contasol SII module for accounting firms with very different profiles. Some recurring patterns:
- Accounting firm with 3–5 clients required to use the SII: the challenge is maintaining several tax IDs active with their respective certificates in the same Contasol installation. Contasol's multi-company management supports this, but requires careful initial configuration to avoid certificate cross-contamination.
- Industrial company with a high volume of received invoices: manually submitting supplier invoices is not feasible; you need to configure automatic import from email or from the purchasing ERP into Contasol, and schedule batch submissions outside working hours.
- Migration from another accounting package: when a company arrives at Contasol from ContaPlus/Sage 50 or from a3/Wolters Kluwer already subject to the SII, the data transfer must ensure that historical invoice types are correctly mapped. Retroactive submissions for the initial period are particularly delicate.
If you are in any of these situations, visit our service page for Contasol implementation and support to see how we approach each scenario.
Most common errors when connecting Contasol to the SII
Experience from multiple implementations allows us to anticipate problems before they occur. The most frequent ones:
| Error | Common cause | Solution |
|---|---|---|
| Certificate not found or expired | Certificate installed under the wrong user profile or expired | Renew the certificate and install it in the machine certificate store, not in the user profile |
| Invalid recipient tax ID | Incorrectly formatted foreign tax ID or fictitious ID on simplified invoices | Review foreign tax ID encoding; use «NOT AVAILABLE» only where the regulation permits it |
| Inconsistent invoice type | Corrective invoices recorded as ordinary invoices | Reconfigure the journal entry types and resubmit the affected records |
| Duplicate record | Resubmission of an already-accepted record without changing its key | Use the cancellation and substitution option instead of direct resubmission |
| Submission timeout | Sending very large batches during peak hours at the electronic office | Schedule bulk submissions outside the 08:00–10:00 window |
Schema updates: the problem that never ends
The AEAT periodically updates the SII XML schemas. Since 2017 there have been several schema versions (the most significant was the update to version 1.1 in 2018, which added investment goods and intra-community records). Each update requires the software to be current for submissions to remain valid.
TeamSystem España — the group to which Software del Sol, the manufacturer of Contasol, belongs — keeps the software up to date with every regulatory change. However, updating Contasol without verifying that your company's configuration is still correct can introduce errors. In networked installations or those with heavily customised charts of accounts, a post-update review is advisable before resuming submissions.
At Summum Sistemas we manage this process for our clients: we test the update in a test environment, verify that test submissions pass AEAT validation, and only then apply the update in production.
SII, Contasol and integration with Factusol
Many companies use Factusol for commercial management (quotes, orders, delivery notes and sales invoices) and Contasol for accounting. The native integration between the two products allows invoices to be exported from Factusol to Contasol with a single click, automatically generating the accounting journal entries.
In an SII workflow, this integration is particularly valuable: issued invoices arrive in Contasol already coded with the correct invoice type, minimising validation errors when submitting to the SII. If your company uses this workflow and experiences frequent rejections, the first thing to check is whether the Factusol-to-Contasol export is generating the correct invoice type in the journal entry.
Frequently asked questions
Is Contasol compatible with all special VAT regimes?
Yes. Contasol covers the main special regimes that affect SII records: the Cash Accounting Special Regime (RECC), reverse-charge transactions, agriculture and livestock regimes, and intra-community transactions. In each case, the journal entry coding in Contasol determines the type of record sent to the SII, so it is essential that the chart of accounts is correctly configured for each regime.
What happens if I submit a record outside the four-business-day deadline?
The AEAT accepts late submissions but flags them as out-of-time. This does not block the process, but may give rise to a penalty procedure. The SII penalty regime (Article 200 of the General Tax Law) establishes fines for each record submitted late or with incorrect data. In practice, the AEAT tends to be more lenient during the first months of adaptation to a regulatory change, but it is unwise to rely on that leniency systematically.
Do SII companies also need to comply with Verifactu?
No. RD 1007/2023 expressly states that taxpayers included in the SII are exempt from the obligation to use billing systems compliant with Verifactu. They are mutually exclusive regimes. If your company is in the SII, you do not need to worry about Verifactu for your own software. You should, however, review the situation of your invoicing software providers if you have clients outside the SII threshold.
Can I use Contasol in the cloud and still submit to the SII?
Yes. The Cloud version of Contasol (from approximately 21 EUR/user/month, indicative manufacturer price) includes the SII module with the same functionality as the desktop version. The digital certificate is managed through access to the electronic office from the user's browser or via an authorised representative. For accounting firms with several accountants working remotely, the Cloud version considerably simplifies SII management, as it centralises submissions and history in a single point.