why does the bank ask for my actual business address and not my postal address

Establishment address is the address from the Business Register, not your correspondence address

The bank asks for the actual establishment address because that is the address where the enterprise is actually established — the place of business operations, not the place where mail is read. That is different information from a PO box or the address of an accountant or virtual office. Banks ask for this as part of their own client due diligence: they want to know where an enterprise actually is located, not just where it can be reached. In onboarding, this is a standard question, regardless of the sector or size of the enterprise.

In practice, this is usually simply the address registered in the Business Register of the Chamber of Commerce as the establishment address. If you have a mailing address that differs from your establishment address — for example because your administration is handled externally — your customer or you yourself still enter the establishment address, and you can provide the mailing address separately if requested. This is the same question that appears in chain dossiers as the establishment address of the enterprise: once correctly recorded, you do not need to reconstruct it each time. If you are uncertain whether your situation (for example multiple establishments) falls under this, that is also traceable back to the question in which countries the enterprise has establishments, which often appears in the same list next to this one.

Where this data comes from: the Business Register Act

The distinction between establishment address and mailing address follows from the Business Register Act 2007, which sets out which data of an enterprise must be registered, including the address of the establishment. That is the data that banks check during onboarding, because it is a verified fact and not a self-reported contact address.