After reverting Service Desk back from HTTPS to HTTP the Support Automation Invite End User link in the email sent is generating an HTTPS URL.
The root cause of this issue can stem from the WEB_CGI_URL option still being set to HTTPS.
SDM 14.1SDM 17.0
The WEB_CGI_URL setting can be accessed in Service Desk under the Administration tab-> Options Manager-> Notifications
Set the address here to HTTP and recycle services.