If you are going to register as autonomo or you are thinking to change your bank the first thing that you will need to check is that the bank that you choose is among the financial entities co-operating with Social Security & Hacienda. 

One pre-requisite to register as self-employed (autonomo) is to have a Spanish bank account to which the Social Security will debit your  monthly social security contribution. You will also need a bank account to pay your tax, specially if you request postponements. 

However not all financial entities based in Spain are included in the list of co-operating banks.

1.Make sure the bank that you select is included in both lists*.

List of banks cooperating with Social Security.

List of banks cooperating with Tax Office.

* Unfortunately that is not all that could go wrong. Some banks do not allow for Social Security direct debits in particular accounts opened with non-business purposes such as saving accounts, etc… Those this is not the common case we have noticed this happening with some ING bank accounts.