Try troubleshooting this issue with these steps:

• Have them check all their spam/advertisement folders for messages from your site's registration system.
• Use the "re-send activation email" tool from the user login screen to have them try receiving the email again
• If neither of those are successful, check your user reports to make sure the user didn't misspell their email address (this happens sometimes!) If you cannot find the user's email, add the created date field and sort by that field - newest first - to see if you find an email that is close-but-not-quite. If there is one there you can edit the user to correct the misspelling or delete that user and ask them to re-register.
• If the user exists in the user report and their email address is correct, add the fields "Email Bouncing" and "Email Bouncing Type" to your report. If a bounced email has been detected and the user has confirmed their email address is correct this may indicate a configuration issue with the user's email server or other underlying problem. Please share the details with RideAmigos support and we will help resolve the situation.