I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others" I'll repost your solution in case you'd like to accept the answer.
Issue:
You were trying to create a group chat in Teams that includes an external guest user using the Logic Apps connector. Initially, it seemed that the "Create a chat" action in Logic Apps did not support adding guest users to a group chat.
Solution:
You found that it can be done if you use the user ID instead of the email address. Here’s how you resolved it:
- First, get the user profile using their internal email address as the UPN (e.g., extrernalemail_gmail.com#ext#@mycompany.onmicrosoft.com). This returns the ID.
- Use the returned ID when creating the chat.
If I missed anything, please let me know and I'd be happy to add it to my answer, or feel free to comment below with any additional information.
I hope this helps!
If you have any other questions, please let me know. Thank you again for your time and patience throughout this issue.