'Call Transfer Failed' when transferring to external number

[mdc2]

Do you have the extension in a Group? and that group set to have an outbound rule in order to get out?

 

[Aegis PS]

Do you have the extension in a Group? and that group set to have an outbound rule in order to get out?

Yes, I granted that extension membership to a group in which other extensions regularly make outbound calls.

 

[mdc2]

I PM'd you. Let me know if you would like me to take a look later.

 

[Aegis PS]

I contacted our SIP provider and they advised I go to SIP Trunks > [trunk name] > Options > Advanced > uncheck the "Supports Re-Invites" option. After doing so, call forwarding is now working.
Oddly enough, the forwarding still does not work when using Ring Groups and the default x000 extension (this could be because the extension does not have any devices provisioned but it did work in v15).
Using a regular extension with forwarding rules after 1 second does work and transfers to the external number correctly.