This endpoint allows a partner to add an API key to one of its accounts from the Partner Portal. A portal user who was removed from the partner or deactivated is refused with INVALID_ACCESS even with a still-valid token. Partner Portal session only: the request must carry the Partner Portal bearer token of a user with the Admin role, and the partner must have AccountCredentialsAccess. The account must be an Active account or sub-account of the partner (or, when PartnerCreationEnabled is on, of one of its child partners). Returns RESOURCE_NOT_FOUND when it is not. Retrieve, add, edit and delete are recorded in an audit log with the Partner Portal user, and the request fails if the entry cannot be written.