An invalid callback URL error occurs when attempting to save Auth0 callback URLs containing wildcards in Mozilla Firefox. This happens because Firefox enforces strict URL validation that rejects wildcard characters in input fields, whereas Chromium-based browsers are more lenient. Resolve this issue by using Google Chrome or another Chromium-based browser to configure and save the allowed callback URLs.

When configuring a callback URL such as <*.sub.example.com> in Firefox, the following error message appears:

One or more callback URLs are invalid

• Auth0
• Callback URLs
• Mozilla Firefox

Firefox enforces stricter URL validation and hostname parsing than Chromium-based browsers. Chromium-based browsers are more lenient with URL characters in input fields, allowing the browser to parse and save the wildcard (*) character without issues.

What resolves the invalid callback URL error in Firefox?

Configure the allowed callback URLs using an alternative web browser to bypass the Firefox validation error.

1. Open Google Chrome or another Chromium-based web browser to configure and save the Allowed Callback URLs.
2. Verify whether the error message is still being received or if a success message appears instead.
3. Validate the callback URL's functionality. 

The Auth0 backend handles wildcard callbacks seamlessly during authentication, regardless of the browser that initiates the login.