Use same email for multiple accounts.
Clients being able to use the same email but have a different user name to sign in. I train youth clients and some parents have more than one child and can’t add an account because they already used the email. I had a client use three e mails to add their child on the app. A different user name would be easier to use in this case. Make an e mail a requirement upon sign up but need a user name to register.