If you are trying to add an SMTP provider and this error message shows up, please check if the location has email reselling settings is enabled in the agency SaaS configurator page.
How to disable Email Rebilling?
2. Once you are in the agency view, click on Sub-Accounts > Search by sub-account
3. Once you locate the sub-account
Click on the sub-account Name OR click on the three dots at the bottom right to Manage Client
4. Scroll down all the way to the bottom to find Email Resell Settings and toggle the highlighted button here to disable Email rebilling.