If you are trying to send a fax and receive the following error message, then there is a relatively simple solution.

{
"errorCode": "CMN-419",
"message": "In order to call this API endpoint for another
extension, one of the following permissions
[OutboundFaxes] have to be granted with
extended scope to the authorized user.",
"permissionsName": "OutboundFaxes"
}

A version of this error message can also be seen when performing other actions via the API as well, and the root cause and remedy is almost always the same. Here are other times you might encounter a version of this error:

* Sending an SMS
* [Reading messages from the message store][1]
* [Accessing a call recording][2]

**The root cause**

This message generally refers to a circumstance when a user is trying to perform an action on behalf of another user, or that only another user is permitted to perform vis-a-vis the specified resource. In layman's terms, a user can only send an SMS (or a fax) from a phone number that has been assigned to them. Therefore, if a user tries to send an SMS (or a fax) from a phone number that belongs to a different user, then you will see the above error message.

**The remedy**

The remedy requires developers to maintain access tokens (or JWT credentials) on behalf of multiple users. So imagine you have the following lookup table:

User | Phone Number | Credential
|-|-|
Luke | (510) 555-1234 | xxxxxxxx
Leia | (510) 555-5678 | yyyyyyyy
Han | (510) 555-2468 | zzzzzzzz

So if Luke wants to send an SMS (or fax) from "(510) 555-2468," then you need to look up who that phone number belongs to, retrieve their credentials, authenticate to the API using those credentials, and then send the SMS (or fax).

[1]: https://community.ringcentral.com/questions/1532/unable-to-create-smsmms-message-in-sandbox-errorco.html
[2]: https://community.ringcentral.com/questions/117120/permission-error-when-accessing-recording-from-ano.html