Users are only getting an error about incorrect username when submitting the registration form

[theorm]

There is a back end error in the logs that bubbles up to the front end:

[impresso.middle-layer] _validateOne throws errors: {
[impresso.middle-layer]   username: {
[impresso.middle-layer]     code: 'NotValidRegex',
[impresso.middle-layer]     regex: '/^[a-z0-9-]+$/',
[impresso.middle-layer]     message: 'username param is not valid'
[impresso.middle-layer]   }
[impresso.middle-layer] } - item: Jo Devaquet

We need a validation on the front end that would prevent users from submitting their registration if the user name does not match the regex.