Some general questions?
Do you work the first time with velo-code?
Where did you find the shown code-snippet?
<a href="sms://+1800605xxxx?&body=I%27m%20interested%20in%20your%20product.%20Please%20contact%20me.">Send a SMS</a>
I can’t seem to get the button to respond, what am I doing wrong?
Of which button is talked about?
I assume that you will need to use an HTML-Component to implement this code-snippet.
Here some links, which could help you to solve your problem…
or try TWILIO…