Login with username as date

Never tried this before, but I have a system where the login details need to be username as a date, such as 2022-11-16, each time i try this I get an unauthorised response, anyone got any idea why?

I have tried sending the username by itself, as a string, and as a formatDate(‘yyyy-MM-dd’), as well as a combination of the two, format date, then convert to string.

The date in the database is stored as DATE, and not as a string.
The Login Form Input, looks like this.

<input type="date" class="form-control" id="inp_username_date" name="username_date" aria-describedby="inp_username_date_help" placeholder="Pick a Date *" required="">

Only work around so far is if I alter the MariaDB DATE to a VARCHAR instead, but that is really not ideal for me.