This frequently asked question explains the initial registration procedure, that is, it applies to entities that access the services of the State Tax Administration Agency (AEAT) for the first time. In the case of the AEAT, the circuit is always the same: first you must process the initial authorization with the AEAT and, once granted, you can request the service at Via Oberta (AOC).

Is this the first time you have accessed AEAT data?

This situation applies if you do not yet have authorization from the AEAT to consult its services. In this case, you must:

  • Request initial registration with the AEAT , and

  • Send for the first time the public key of the electronic seal certificate that will be used to make the queries.

Therefore, this initial registration procedure with the AEAT is prior to and essential for any service request through Via Oberta (AOC).

If you do not have prior authorization from the AEAT, it is not possible to activate or use the service at Via Oberta.

Prerequisite: have an agreement with the AEAT

Before initiating the registration request for AEAT services, you must have a valid agreement with the AEAT that authorizes the consultation of data, duly approved by the competent body that determines it.

This requirement can be met by:

  • Adherence to an AEAT-FEMP collaboration agreement , or

  • The signing of a specific agreement for the transfer of tax data with the AEAT

It is important that you check which purposes (tax or non-tax) the agreement you have in force covers, since only consultations that are covered by it can be authorized.

In general, the two AEAT-FEMP agreements cover practically all the tax information needs of the local world. However, if you have a specific need that is not included, you can always choose to sign a specific agreement.

Once your entity has joined the agreement, you must indicate its name and the date of accession or subscription when processing the AEAT service request form at Via Oberta (AOC).



a) AEAT-FEMP collaboration agreements
In the case of the AEAT-FEMP agreements, you only need to adhere to one of the two current agreements , depending on the type of consultations you want to make (tax or non-tax purposes).

Currently, the following agreements exist:

  • AEAT–FEMP collaboration agreement on the exchange of tax information and collaboration in revenue management with local entities (consultations for tax purposes)

  • AEAT–FEMP collaboration agreement on the provision of tax information
    (consultations for non-tax purposes)

The details of the accession process, as well as the areas and procedures of collaboration, are described in the clauses of each agreement, where the conditions applicable in each case are specified.

You can consult all the information on the website corresponding to the purpose of the procedure, in the Agreements with Local Entities section, accessible from the following links:


AEAT website for tax purposes


AEAT website for non-tax purposes

If you want to check if your entity is affiliated to any of the aforementioned agreements, the AEAT website has a list of local entities affiliated to the AEAT-FEMP agreements .

b) Specific agreement for the transfer of tax data
As an alternative, your entity may have a specific tax data transfer agreement signed directly with the AEAT, which allows you to make the inquiries you need.

In this case, you must verify:

  • What purposes and procedures does the agreement cover?

  • That the queries you want to make are correctly legally protected by their content.

Which form should I use?

To make the initial registration, you must use the AEAT's own form to request information through web services.

You can download this form from the corresponding website according to the purpose of the procedure (tax or non-tax), in the Forms, guides and models section, accessible from the following links:


AEAT website for tax purposes

You must complete all sections of the form, following the instructions indicated.

The form itself includes, at the end of the document, detailed instructions for filling in each field, which we recommend you follow to avoid errors or requests for corrections.

In the form you must indicate, among other things:

  • The purposes and procedures for which access is requested.

  • Web services and access methods.

  • The reason for presentation (initial discharge).



How and where is the AEAT form submitted?

You must submit the form and public key through the electronic registry of the AEAT headquarters , along with the required documentation, using the corresponding identification system:



You can access the registry indistinctly:

  • From the specific website according to the purpose of the procedure (tax or non-tax):
    a) Tax purposes



AEAT website for tax purposes

b) Non-tax purposes



AEAT website for non-tax purposes

  • Or, from the general catalog of procedures of the AEAT electronic office, through the route: Home > All procedures > Other services > Public Administrations, where you can filter the procedures according to whether they are for tax or non-tax purposes:

a) Tax purposes



AEAT website for tax purposes

b) Non-tax purposes


AEAT website for non-tax purposes

In both cases, accessing the submission process redirects you to the generic Electronic Registration form for document submission , in HTML format.



Example of generic form available in the electronic registry of the AEAT headquarters

This form:

  • The corresponding procedure and formalities are already automatically preset , depending on the purpose you select (ZA04 tax purposes or ZA05 non-tax purposes).

  • It allows you to attach the AEAT initial registration form within the procedure, previously filled in and signed in PDF, as well as the required documentation (public key of the certificate in ZIP format).

Therefore, you do not need to manually select the procedure or formality, as they are automatically included when you access the AEAT's electronic office from the enabled links.

The operation of the generic electronic registration form is explained on the help page of the AEAT's electronic office.

Once you have registered your request:

  • An acknowledgement of receipt is generated with a Secure Verification Code (CSV).

  • You can consult the file on the AEAT's electronic office.

Subsequently, the AEAT analyzes the request and, if applicable, authorizes access to the data you have requested.

What documentation must be submitted?

To process the initial registration with the AEAT services, you must present the following documentation:

  • The initial registration application form for the AEAT web services, duly completed and signed, in PDF format.

  • A ZIP file with the public key of your entity's electronic seal certificate, in .cer format.

If any of these elements are missing, it may result in amendment requests and, therefore, delay processing.

Amendments and requirements from the AEAT

If the AEAT detects that the application submitted is incomplete or requires any correction, it will notify you of the amendment requirement.

In this case, you must submit the amendments through the authorized procedure of the AEAT electronic office, within the period indicated in the request:
Respond to requests or submit documentation related to a document received from the AEAT



AEAT website for access to the procedure

If you need help submitting an amendment or responding to a request, you can consult the following frequently asked questions on the AEAT's electronic office:
How to respond to requests or submit documentation related to a document received from the AEAT

How and when should the public key be sent?

In the case of initial registration , you must attach the public key of your entity's electronic seal certificate along with the application form, which you must submit through the electronic registration procedure enabled at the AEAT's electronic headquarters.

To take into account:

  • You will need to attach the public key in a ZIP file , in .cer format.

  • This is the first sending of the certificate to the AEAT.

  • The seal certificate must be valid and will be the one used to access queries on the AEAT's web services.

This sending of the public key is exclusive to the initial registration process. In subsequent procedures (such as the communication of new purposes), it will not be necessary to attach it again if the certificate has not changed.
How to download the public key of the new electronic seal certificate from the AOC subscriber folder

Registration and official authorization from AEAT

Once the AEAT has analyzed the request and authorized access, it will notify you by email, indicating the effective registration and the specific data to which you will be able to access.



Example of communication of registration and official AEAT authorization

From this moment on, you will be able to request the corresponding service through Via Oberta (AOC) , in accordance with the authorizations granted to you by the AEAT.

Final reminder

  • The initial registration always includes the first sending of the public key.

  • Without prior authorization from the AEAT, you will not be able to request the service at Via Oberta.

  • If you plan the requirements in advance (agreement, certificate, purposes) you will avoid requests and possible delays.

Additional information