If it doesn't work then open case , but I reckon your doing something wrong
Try doing it via https://www.open-telecom.co.uk/products-services/opentap-to-mobile-text-sms-and-email-messaging-gateway/
Expensive tho
Well then use the maintained tap service , but it's expensive not worth it for a general txt
Your better off using outputs and connecting to a gsm dialler and get a contract SIM that you don't have to top up, just have an SMS max
Then keep the phone dialer aswell