V20 Teams Direct Routing - Shared Calling Outbound Call Fails - "Mapping for Teams number... not found!"

[ebacademy]

Hello everyone,

I need help with a Microsoft Teams Shared Calling issue on 3CX v20.
We have followed all the documentation we can find, but outbound calls from the shared calling resource account are failing.

Background & Goal

• System: 3CX v20 (Self-hosted)
• License: 16SC ENT
• Integration: Microsoft Teams Direct Routing
• Goal: We are implementing Teams Shared Calling. The goal is to allow multiple Teams users to make and receive PSTN calls using a single phone number and calling plan, which is managed by a Teams Resource Account.

How we believe it Should Work: a Teams user with a shared calling policy places an outbound call. Teams then sends the call to 3CX via Direct Routing, presenting the identity of the Resource Account (e.g., mainlinera@ with number +1XXXXXXXXXX). 3CX should then recognize this synced user, apply the appropriate outbound rules, and route the call to the PSTN.

The Problem & The Error
When a user tries to make an outbound call, it fails instantly. The 3CX Activity Log shows the initial generic error:
"Failed to build source endpoint!"
the verbose log gives us:
"Mapping for Teams number +1XXXXXXXXXX is not found!"
This error occurs even though we have a user for mainlinera@ that is correctly synced from M365 and has the +1XXXXXXXXXX number populated in its mobile field. The system is not finding the mapping. The call is then rejected with:
"603 Decline / Caller is forbidden"

Troubleshooting Steps Taken

1. Manual User Creation (Initial Attempt): We first created a manual user in 3CX with the email address set to the Resource Account's UPN (mainlinera@). This did not work.
2. Manual User + Outbound Caller ID: We added the Resource Account's phone number to the Outbound Caller ID field of the manual user. This also failed.
3. Full M365 User Sync: Believing the issue was with manual users, we implemented the sync method:
   • We confirmed the Resource Account (mainlinera@) was in a group that is synced with 3CX.
   • In the Microsoft Entra admin center, we added the assigned phone number (+1XXXXXXXXXX) to the "Mobile phone" field of the Resource Account user.
   • We ran the M365 sync in 3CX and confirmed the user now appears in 3CX with the M365 icon, and the "Mobile" field is correctly populated with the number.
   • Result: The call still fails with the exact same "Mapping for Teams number... is not found!" error.
4. Permissions and Outbound Rules: To eliminate routing as a cause, we checked the following:
   • The synced user is in a Department where the assigned Role has the "Make outbound calls" permission enabled.
   • We created a new, high-priority Outbound Rule at the top of the list that explicitly allows this user's extension to call any number.
   • Result: The call still fails with the same error.

Questions
Why is the Teams number mapping failing when a perfectly synced M365 user with the correct mobile number exists in 3CX? It seems the Teams integration module is not seeing or querying the synced user's number correctly.

Has anyone else successfully implemented Teams Shared Calling with v20 and a Resource Account? Is there another configuration area for this number mapping, or could this be a potential bug?

Any advice would be greatly appreciated. Thank you!

 

[TerryKC]

Try configure the number to the Microsoft accounts "office phone" rather than mobile

 

[ebacademy]

Try configure the number to the Microsoft accounts "office phone" rather than mobile

Unfortunately, this does not work.

 

[Charles_3CX]

Unfortunately, this does not work.

Please see the requirements here: https://www.3cx.com/docs/microsoft-teams-integration-faqs/

Ensure that the Number entered in the 365 user account's Office phone number is in E. 164 format and that the exact number is entered under the user's 3CX account settings for their outbound caller ID. Then, you will need to re-generate and re-run the user script.