3cx Version 20 with m365 sync, there is no clear path on how to set a custom extension and then sync the m365 user

[xosystems]

Hello everyone,
I hope you’re doing well.
We need to migrate from an old PBX to 3CX, each user has a specific phone extension.

We’ve successfully deployed 3CX v20 Enterprise on Azure with Microsoft 365 integration.
The 3CX dashboard reports that the firewall configuration is OK, and M365 sync with message: “Status OK. Real Time Notifications from 3CX to Microsoft 365 are working and in sync.”

What we’ve done:

• Installed 3CX v20.
• Verified firewall checks
• Enabled M365 integration (UPN matches exactly).
• Using selected Users on 3CX / Admin / Users / M365 with
  • Enable SSO
  • Sync user photo
  • Sync Personal Contacts
  • Sync user account details (also tried without)
    • Account Enabled -> Disable Extension
    • GivenName -> First Name
    • Surname -> Last Name
    • Mail -> Email
    • MobilePhone -> Mobile
    • Business Phones -> Outbound Caller ID

What is working:

• If we select a user from 3CX / Admin / Users / M365, the user is successfully added on 3CX / Admin / Users with elements such as photo, presence sync, etc

What isn’t working:

• We cannot assign a custom extension to a new user and have it synchronize to Azure Entra ID/M365.
• We cannot return a deleted user on 3cx / Admin / Users from m365

How we’re creating users:

In 3CX Management Console → Extensions → Add New Extension:

• Extension: Custom (e.g. 1501)
• First Name, Last Name
• Email = Azure Entra UPN (exact match)

XAPI Comparison
We have also tried to cross-check differences between a successfully synced user from m365 and a user that was first created on 3cx
"/xapi/v1/$metadata#Users(Greetings(),ForwardingProfiles(),ForwardingExceptions(),Phones(),Groups())/$entity"

• User A: Originated in M365 → JSON includes "Tags": ["MS"]
• User B: Originated in 3CX → JSON includes "Tags": []

We attempted an unsuccessfully xapi patch to the Tags

What we need:

• Guidance on configuring 3CX so that custom extension assignments push correctly into M365 contacts/users.
• How do we return a deleted user?
• Are there any specific permissions, policies, or mapping steps required?

Thank you in advance for your insights!

 

[yesss-de]

When i did that for our dutch branches recently I imported dummy users with the correct email adresses/UPN via csv
all i gave them were the bare required fields extension, mail, name(test), surname (test)...
after that i enabled the users in the M365 options and added them to sync and all the data was synced