Hi @emboywondr, 
I understand this can be frustrating. Let me know in the replies below what product you're using since that will change the process. 
Sometimes users have multiple IDs and they aren't synced with the ID in your system. Some options when this happens: 
-Try uninviting and inviting, or deleting the request and creating a new request. 
-You can have your client create a new profile before you delete and invite them again. 
-You can also ask them to use a different email to create a new account. 
-If a new email isn't an option, they should to contact the number for your product to get an account and password reset on our end. 

Keep me updated in the replies on what has worked or not.