Cannot transfer call from bot in Teams client

[rvleeuwen256]

Hi,

During some time now we (and our customers) are unable to transfer an established call (between a bot and a Teams user) to another Teams user using the Transfer button in the Teams client. This did work in the past. Only recently we were notified about this problem by one of our customers.

Scenario:

1. Bot calls Teams-User1
2. Teams-User1 answers call and talks to bot.
3. Teams-User1 transfers call to Teams-User2. (this is what fails now)
4. Teams-User2 answers call and talks to bot.

In step 3 you get a 'Transfer failed' message in the Teams client (see screen shot). On the bot side there seems to be no indication that something goes wrong. Both a direct transfer as well as a consultative transfer fail.

An example of a call which could not be transferred:
Teams-CallId = 45003980-53f7-40d4-8182-04ef23282313
Time-of-transfer = 2025-12-29 13:24:50 UTC

Library versions:

• Microsoft.Skype.Bots.Media 1.31.0.226
• Microsoft.Graph.Communications.Calls.Media 1.2.0.15533
• Microsoft.Graph 5.94.0
• Microsoft.Graph.Core 3.2.4

Hopefully you can give us some insight in what goes wrong, because this is a use-case that is used by multiple customers of our SaaS-service.