Go to the Teams Admin portal
Under Meetings, Meeting policies, check which policies you have
Make sure the meeting policy you are using has the following enabled
Next, make sure that policy is applying to the users
Under Users, click on View policies. You may need to click on the gear icon to show the column.
In my case, RestrictedAnonymousAccess was applying and overriding the settings in Global (Org-wide default)
Use the following post on Microsoft to fix
https://docs.microsoft.com/en-us/microsoftteams/meeting-policies-restricted-anonymous-access
Depending on the size of your organisation, you can use the Users page to assign the policies in bulk.
Get the user to sign out and back into the Teams client
