SMS - Phone number doesn't belong to extension

I'm using the Ring Central api to send a SMS message. All is good in the Sandbox where I can freely send on SMS messages.

My application is now approved for Production, but when I use the Production account information I can authenticate and get a token, however when I try to actually send the SMS message, I get the following response:

{

"errorCode": "FeatureNotAvailable"

"message": "Phone number doesn't belong to extension"

"errors": [

1]0: {

"errorCode": "MSG-304"

"message": "Phone number doesn't belong to extension"

}

}

I don't actually use an extension to authenticate or send the SMS both from the Sandbox or Production.

Any thoughts would be great!!