promptLogin() shows the incorrect form

I moved from a custom signup form to the default signup form, this works fine when using the built in member bar to login/signup. But when promptLogin() is called (from a sign-up button on the home page), the old custom signup form is shown instead of the default signup form (regardless of the LoginOptions that are passed to it). Is there a way to fix this?

When you say custom, do you mean Custom or Corvid as shown in the three choices here.
https://support.wix.com/en/article/about-the-member-signup-form

If you have used Corvid, then you need to change the member signup settings to your Corvid lightboxes.
https://support.wix.com/en/article/corvid-enabling-custom-site-registration

Then you need to add the options to promptLogin for which option you want to show first.
https://www.wix.com/corvid/reference/wix-users.html#promptLogin

Prompt the current user to login with given options

import wixUsers from 'wix-users';

// ...

let options = {"mode": "login", "lang": "es"};

wixUsers.promptLogin(options)
  .then( (user) => {
    let userId = user.id;           // "r5me-6fem-45jf-djhe-484349"
    let isLoggedIn = user.loggedIn; // true
    let userRole = user.role;       // "member"
    return user.getEmail();
  } )
  .then( (email) => {
    let userEmail = email;          // "user@something.com"
  } )
  .catch( (err) => {
    let errorMsg = err;             // "The user closed the login dialog"
  } );

If you have used a Custom form as stated here, for which you must have the Wix Members app added to your site.
https://support.wix.com/en/article/creating-a-custom-signup-form-for-your-members-area

Then make sure that you have changed your member signup settings to Custom and not still on Default.
https://support.wix.com/en/article/editing-your-member-signup-settings-for-the-default-form

Thanks so much for the response, I found my answer and feel quite silly! I am working collaboratively with a designer and the sign up button had been set to link to the old custom sign up form. The code I wrote to show the default sign up page was not being called and, instead, the link that was set in the button was being followed :sweat_smile: