Miscellaneous topics that do not fit into specific categories.
Hi there, Brendan! This is Marc. Thanks for providing those details. Based on what you've described, here are a few approaches we can try.
First, go to https://admin.microsoft.com, sign in with your admin account, and navigate to Billing > Licenses to confirm how many are available and assigned. Then go to Users > Active Users, select the user you're trying to add, and click Manage product licenses to assign one manually. If all six licenses are already assigned, double-check for any unused or inactive accounts that could be freed up.
If everything looks correct and it still blocks you, try refreshing the license list or contact Microsoft support via https://support.microsoft.com/contactus for further help.
Let me know how it goes.
Best regards,