Mitel 6869 Call Waiting limited to 2 Calls

[sike]

Hi All

I have just deployed a Mitel 6869 to replace a Snom 760 at the reception. With the Snom if the receptionist was on the phone, the second call and a third call could come in. Now with the Mitel 6869 the phone seems to be limited to 2 calls. If the receptionist already has two calls, the thrid call is 'busy'.

I have also tried adding a Softkey for 'Line 3'

The Mitel Phone is running: V4.2.0.2023 SP2, 07/2016

Asterisk 11.

I have read through the Mitel Admin guide, and can't find a thing. Any help would be greatly apreciated.