'Call Transfer Failed' when transferring to external number

[Aegis PS]

We have a series of menu options set up with Digital Receptionist. One of the options on an IVR is set to dial a Ring Group with a Ring Time of 1 second that is set to Forward to Outside Number upon no answer. Before upgrading to v16, this number seemed to work fine but now it does not.
Calling the external number directly works fine. It does not work when I go through the menu options and choose the option that dials the external number, does not work when I dial our main number then the IVR's extension and choose the option, and does not work when I dial the IVR's DID and choose the option. All Firewall tests passed and calling is working fine otherwise.

Is there an attribute/flag that needs to be set? Is there an easier way to set an option to forward to an 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.