After a bit of research, it looks like the current version of the code that powers our form specifically has a conflict with adding a few HTML elements to the success message. Here's the elements that will be hidden if you try to add them to the message:
A quick and easy workaround for your case would be to use an <input> element that is not part of a form. For example:
<input type="button" value="This text is displayed" />
Please let me know if you have any questions!
Elijah G. API Support Engineer
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