When I fire the API to send a message - I get “Phone number doesn’t belong to extension” What am I doing wrong?

Check out this dev guide and see the quick start sample code to begin with.

Please help me how to get Business SMS menu into Telus flavor of RingCentral - Screenshot attached. 

Here is non Telus account for reference 

Unfortunately, I cannot help with this kind of issue. It’s not related to RingCentral API platform or app development/programming.

Please submit a customer support ticket to get better support.