Hi,
Based on the error information you have provided, I suggest you follow the steps below to troubleshoot:
- Sign in to Microsoft 365 admin center
make sure the Business Standard license is still in active.
Also you can take a screenshot and send it to me and I'll be happy to check it for you!
- Try to reassign the license and wait for some time for it to take effect.
- Use your browser's inPrivate mode to access OWA to avoid the effects of caching.
- Check if the account can log in to Microsoft 365 Portal to make sure the issue is only in OWA.
Hope this helps!