Thank you Patrick for your assistance, and what a simple solution it landed up being.
Adding .txt to the URL forces it to plaintext, so a simple url alteration from
https://zoomconnect.com/app/api/rest/v1/sms/send-url/add6f984-xxxx-xxxx-xxxx-xxxxxxxxxxxx?recipientNumber=27767480000&message=Testing
TO
https://zoomconnect.com/app/api/rest/v1/sms/send-url/add6f984-xxxx-xxxx-xxxx-xxxxxxxxxxxx.txt?recipientNumber=27767480000&message=Testing
And now its all working. Also it is not actually a Wappler bug but more a problem in the API return where the provider is sending back json with no json content, so not a Wappler bug afteral.