@User you also need to add the custom form fields id on the init for the backend side. If you see the docs for adding custom fields, that page has two sections: - frontend config change: https://supertokens.io/docs/thirdpartyemailpassword/common-customizations/signup-form/adding-fields#front-end - backend config change: https://supertokens.io/docs/thirdpartyemailpassword/common-customizations/signup-form/adding-fields#back-end Please make sure you are doing both 🙂