Good day Ken,
When a contact appears with Invite beside their name, Teams may be identifying that person as being outside your organization or as not having an active Teams account. If the person doesn't have a Teams account, Teams normally sends an invitation for the person to create an unmanaged Teams account. Communication can also be restricted by the external access settings of either organization.
Please try these steps:
Open Teams > Chat > New chat.
Enter the contact's full email address in the To field instead of searching by name.
If the contact appears, select it and send a message.
If the contact still cannot be selected:
1/ Ask the contact to check their email and accept any Teams invitation they have received.
2/ Contact your organization's IT administrator and ask them to verify that:
Note: In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support
External Access is enabled.
The contact's email domain isn't blocked.
Communication between both organizations is allowed.
If you need ongoing collaboration with the external user, your administrator can also add them as a guest, then the user can accept the invitation and participate in Teams chats.
Additional information is available in the following resources:
Add or invite people outside your org to a chat in Microsoft Teams | Microsoft Support
IT Admins - Manage external meetings and chat with people and organizations using Microsoft identities - Microsoft Teams | Microsoft Learn
Guest access in Microsoft Teams - Microsoft Teams | Microsoft Learn
I hope this information is helpful. If you have any questions or need further support, please don’t hesitate to reach out at any time.
Thank you for your patience and understanding.
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