If you manage database(s) for a customer, it's not enough to manage it/them in SAP Business One. You must also delete the registration(s) of the respective database(s) in the portal.
Please log into the Boyum Portal and find the customer's license:
A new window opens:
Depending on the license type and extra purchased databases, the total number of databases is showed as "Allowed". "Active" refers to the number of active databases.
Click the "x" to delete. Once done, press "Save" /"Close". There is now extra space for new databases.
NB: Please note that partners can't manage databases for their internal partner licenses. In case you need anything edited, please contact firstname.lastname@example.org for assistance.