What is always mandatory is the ability to issue an invoice for any profitable activity—otherwise, it would be considered working off the books. To do this, it is necessary to be registered in the census of business owners, professionals, and withholders through the census registration declaration, which can be completed using form 036 or 037.
This document notifies the authorities of the activity you will engage in, as well as the taxes and informational returns you are required to file while carrying out this activity. To request form 036/037, it is essential to have a tax identification number (NIF).
Form 037 (simplified census declaration) is for individuals who meet specific requirements set by the Tax Agency.
This certificate is required before receiving any payments. You can find everything you need to know about these forms here.