Call Forwarding API

Can you revise your question? I have no idea what you want to achieve, or what is the exact problem.

I have 5 phone lines with Ringcentral. 1 line is a masked number where clients call in, this number gets transferred to my other 4 lines (whichever is not busy), I believe it's called the Call Queue Group.

I want to be able to transfer the masked line to an external number. I was able to achieve this in sandbox mode by deleting the forwarding number and creating a new one with these:

https://developers.ringcentral.com/api-reference/Call-Forwarding/deleteForwardingNumber
https://developers.ringcentral.com/api-reference/Call-Forwarding/createForwardingNumber

But once I tried it in Production, it gives me the error:

RingCentralSDKHttpApiException: Device number cannot be deleted from the forwarding number list

I also tried to update the forwarding number (which currently points to the primary number of the 4 lines) but also fails.

So pretty much,

Sandbox:
Masked Line -> Delete Forwarding Number (Success) -> Create Forwarding External Number (Success) -> Calls Being Forwarded

Production:
Masked Line -> Delete Forwarding Number (Fail)
Masked Line -> Update Forwarding Number (Fail)

Sorry for the long delay. Got stuck at other tasks.

So the problem is that you can only use those APIs to manage (delete and update) forwarding numbers, NOT forwarding to other's phones (see attached image)

The behavior is the same for sandbox and production accounts.

I will update if and when I have a solution to this problem.