Registration form fails with 404 in Volto

[rohnsha0]

Describe the bug
The registration form in Volto is failing because it doesn't include the required username field when submitting to the backend API, resulting in a 404 error. The form currently only sends fullname and email fields, but the backend API requires an explicit username field.
When submitting the registration form, the following error is returned:

{
  "error": {
    "errors": [
      {
        "field": "username", 
        "message": "Property 'User Name' is required."
      }
    ], 
    "message": "Error in fields. Property 'User Name' is required.", 
    "type": "WrongParameterError"
  }
}

To Reproduce
Steps to reproduce the behavior:

1. Navigate to the registration page (/register)
2. in the fullname and email fields
3. the form
4. the 404 error in the network tab

Expected behavior
Since the email field description states "This will be your login name", the form should automatically use the email as the username when submitting to the API:

Screenshots

Software (please complete the following information):

• Volto 18.8.1
• Plone 6.1.1
• plone.restapi 9.13.3
• CMF 3.7
• Zope 5.13
• Python 3.12.9 (main, Mar 17 2025, 23:25:08) [GCC 12.2.0]
• PIL 11.0.0 (Pillow)

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[davisagli]

Also related: #5951. We need to make it work when use_email_as_login is True and also when it is False.

[addymistrel]

I have gone through this issue and i believe i can solve it so can you assign me this issue.

[rohnsha0]

@addymistrel A PR is already open...
See #6988

[stevepiercy]

@addymistrel we don't assign issues. Please read and follow First-time contributors, especially Things not to do, Contributing to Plone, and Contributing to Volto.