Latest mobile app should work (I think, not referencing the guides) with that release of MiCollab.
If it is logging in correctly but not registering there are a multitude of potential problems.
First is your DNS setup - if you are testing this on Wifi at your office/location try disabling Wifi and then making sure that teleworker is enabled on the account.
If the issue still occurs try sending problem report from the app. You will find it on the server under View Log Files listed as Feedback with names and date after that. Make sure you download as it is a ZIP.

@AlphaMann no issues with the configuration. DNS, SSL Certs etc all ok.
As i said it works on (version 8.1.49 (Build 22) without any issues.
Problem is with the latest app version (version 8.1.211 build 123).
there is no way i could get hold of an older app right ? its simply not available on app store...
i could fix this by upgrading the server but i`m just wondering if there is any other fix...

Title

MiCollab Mobile SIP softphone will no longer connect after mobile client upgraded to 8.1.111 (or above)

Symptoms


Mobile clients will often upgrade automatically from the App Stores.
After mobile clients are upgraded to version 8.1.111 (or above), it may become apparent that the SIP softphone will no longer register.

Collecting the feedback logs from the mobile, then checking the uca log, will show:

REGISTER ->
<- 200 OK
SUBSCRIBE ->
< - 403 Forbidden


Environment

MiCollab.
MiCollab Client.
MiCollab Mobile Client.


Cause


MiCollab Mobile client 8.1 adds support for MiVB SIP hotdesking.
The mobile client will attempt to subcribe for hotdesk events, if the previous MiVB REGISTER response includes P-Login: mihotdesk.

The Subscribe will fail in this scenario:
•MiVB version is earlier than 8.0.
•MiVB CoS associated with the MiCollab SIP softphone has Hot Desk Login Accept enabled
•MBG version is earlier than 10.1
•MiCollab Client Server is earlier than 8.1
•MiCollab Mobile Client is 8.1

Resolution

A simple workaround is to try disabling the Class of Service option (mentioned above)

The recommended resolution to ensure full compatibility and to ensure full feature availability, is to upgrade MiCollab, MiVB and MBG to the latest versions.
•MiVB version is recommended to be at least 8.0.


•MBG version is recommended to be at least 10.1.


•MiCollab version is recommended to be at least 8.1.

If its not broke tweak it..

@TLDuk i will try that and let you know.
Cheers for the info.