When a member reports that he created a white label and a sub-user account but couldn't see anything when he tried logging into it. Check first if the sub-user is linked with a company. Please see the image below as an example:
Member sometimes forgets to link the company to the sub-user account which is why they cannot see the dashboard of their client.
If the client mention which company should be linked to the sub-user they have created, you can edit the sub-user account to link it and asked the member to try it out again.