The first thing to check, is to make sure you added them as a remote or dual client, and not an in-person client. In-person clients are managed 100% by you, the coach, and as a result do not receive access or an invitation to the client app. If you'd like them to receive access to the app, change them to a remote or dual client, and an invite will be automatically sent to their inbox.
(In the add and edit client window, there is a full breakdown of the client types underneath the option. Be sure to read the 3 options to make sure what is best when you add clients.)
If they accidentally deleted their first invitation email, find the client and either copy the invite link to send manually or resend the invitation all together.
If you've exhausted all of these options, don't hesitate to reach out and we will be more than happy to get you squared away.