Moved to Tableau Server Forum space for more visibility.
Two thoughts come to mind:
1. Site names are case sensitive. I.e. "Site1" in the URL is not the same as "site1".
2. Have you tried the html code from this KB:
The test will help to understand if the problem is with the code or how parameters are being specified.
Otherwise, I'd contact firstname.lastname@example.org
Let me know if this helps!