Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi MarkF1955,
Thank you for posting your issue on Microsoft Community forum. May I double confirm have you expand the Apps section on Licenses and Apps page to check whether the Exchange Online (Plan 1) box selected?
To do this in the admin center, go to the Users > Active users page.
Select the row of the user that you want to check the license.
In the right pane, select Licenses and Apps.
Expand the Apps section, select the boxes for the Exchange Online (Plan 1) license to assign, then select Save changes.
Wait for some times to check this issue.
Here is the screenshot for your reference:
If it is already selected then try to un-assign the Business Basic license from newly created users and wait for some times to re-assign it to see whether the problem still occurs.
Moreover, please provide us with detailed screenshot about the License and apps page and error message via the Private Message for further analysis.
Your patience and understanding will be highly appreciated. Have a nice day and stay safe!
Best regards,
Shyamal