Hi there, when looking at your distributions, do you see any of the error messages referenced in the below support page?
https://www.qualtrics.com/support/survey-platform/distributions-module/email-distribution/email-distribution-error-messages/
Otherwise, you might want to get in touch with Qualtrics Support.

Hi Tom,
Thanks for your help. Yes, it has been resolved after contacting the support team as there was no error code hence I was unsure the problem.
Thanks again.

Hi! 

I know you probably aren’t still checking this but if you happen to see this can you please let me know what Support’s resolution was? I have everything set up normally but now All my distribution email invites fail and there is no error code so Support hasn’t been entirely useful to me.

Thank you!

Rion