When you send a user invitation, it is automatically generated by CrowdWorks. This means that the sender of that email is [email protected] + your name.
For example:
"Amanda Johnson (via CrowdWorks) <[email protected]>"
What to do:
Check you have sent the invitation to the correct email address
The invitation subject line is "Amanda Johnson has invited you to your company name". You should suggest that your contact searches with that term in their inbox
Guide your contact to check their spam folder (it can also end up in promotions, socials, or forums in Gmail)
Make sure the contact has not blocked "[email protected]" by accident
Withdraw the old invitation and send a new one