Anyone know how to fix this typescript type error? Should I include all the key?

async function formHandler(formData: FormData) {
    'use server';

    register({
        user_email: formData.get(FormKey.Email),
        user_name: formData.get(FormKey.Username),
        user_password: formData.get(FormKey.Password),
    } as RegisterProps);
}

<form className={'flex flex-col gap-4'} action={formHandler}>

Typescript error:

Type (formData: FormData) => Promise<void> is not assignable to type string | DO_NOT_USE_OR_YOU_WILL_BE_FIRED_EXPERIMENTAL_FORM_ACTIONS[keyof DO_NOT_USE_OR_YOU_WILL_BE_FIRED_EXPERIMENTAL_FORM_ACTIONS] | undefined