Is there an issue with this? SMS enabled on our Authy plan but getting this error below Authy API key:

"The API key is valid, but does not have SMS enabled or SMS is not available on the Authy account's plan. Enable SMS with Authy or uncheck text messages from the settings below."

Hasn't been working for us for many weeks, possibly since latest update and can't figure out why?

This sounds like an Authy account issue.  It’s saying you are not entitled to send text messages.  That would be something you need to ask Authy about. 

Please contact Authy for assistance as sounds like something is wrong with the plan.

Will do, thanks!