Thanks for posting, @David_Smith!
The special REST API format for Hyperlink tiles makes the request directly from your browser. The SharpTools servers are not involved at all.
The problem is modern browsers will block requests made across two different origins (domains) if the API that is being called doesn’t return a CORS header. In this case, IFTTT’s webhook API is not returning any CORS headers at all which is causing the issue.
What we are proposing is adding an option to the Hyperlink tile REST API syntax which would route the request through our servers to workaround the CORS issue. (Again, the requests currently go directly from your browser to IFTTT)