If a third party (such as an advertising agency) wants to verify their client's commercial administrator, first they need to grant Administrator Business Manager access to the person from the agency who will do the verification (see article).

Ideally, the person who does the verification should have access to an inbox with the client's domain so they can receive the verification code there.

If they don't have access to an inbox with the client's domain name, we recommend that they be in contact with someone from the business so they can quickly send them the verification code.