Problems with external Users in Teams after license changes

Hello,

We changed our license last week from the E3 plan to
Microsoft 365 Business Standard.
Since then we have had a few problems.
In Teams, external users are shown as unknown and we can't chat and call externally.

We have already reapplied the license and also pressed logout from all devices.
after the new login the problem persists.

Thanks for the help in advance.