400 Bad Request from captcha API

## Bug description
When incorrect captcha is given. Even though it shows incorrect validation message, 400 bad request is thrown.

A clear and concise description of the bug.

## Reproduction steps

1. Go to Sign Up Page.
2. Fill all the form inputs.
3. In captcha, give incorrect value.
4. Click the sign up button.
5. See 400 bad request error from the console.

## Expected behavior
It should show validation message but should not throw error from the API.

## Is your portal managed or self-hosted?
Self-hosted

## Release tag

Release 18

## Environment

- Operating system: [e.g., iOS]
- Browser: [e.g., Google Chrome, Safari]
- Version: [e.g., 22]

## Additional context


Start at the sign-up page and reproduce the incorrect-captcha submission against the captcha API, observing the validation response and the console error. Trace how that response is handled and verify that the validation message remains visible without an unhandled 400 error.

Written by the indexing model from the issue text.