A participant did not receive the invitation email....

There are several possible causes: the e-mail address may be incorrect or blocked by anti-spam (especially if it is a company e-mail).
Go to the Monitor my Secret Santa page on your event page:

• Change / Correct the participant's email
• Send back an email

Still not received?

This is very rare but some anti-spam systems are particularly restrictive and require validation by Captcha (i.e. Mailinblack.com, etc.):
*Request to add confirmation AT my-secret-santa.org address in the contact white list of the recipient

• Go through a less restrictive email address and then forward the email to the desired address (without trying to consult the draw, of course

Updated on: 13/11/2020