If you have not received your welcome email, firstly, check your junk mail. If no email is there:
As an Admin User, go to the user dashboard and make sure they have been invited, and confirm their email is correct:
If the user didn't see the email, ask them to go to the Parchment login page and try logging in with their email (that was used when inviting). If the account exists, they will be sent an OTP code to their email.