Flux Woo Subscription - disable create account/password for known users.

flux.php

/**
 * Flux checkout - remove password field.
 */
 function iconic_flux_remove_pass_field( $fields ) {
	unset( $fields['account']['account_password'] );
	return $fields;
}
add_filter( 'woocommerce_checkout_fields', 'iconic_flux_remove_pass_field', 9999 );

/**
 * Flux checkout - Disable customer login requirement.
 */
function flux_remove_customer_login_requirement() {
	return false;
}
add_filter( 'woocommerce_checkout_registration_required', 'flux_remove_customer_login_requirement', 100000 );

/**
 * Remove `createaccount` data from checkout data so it doesnt trigger the `Login to your account` error.
 */
function flux_remove_createaccount_data_for_known_users( $posted_data ) {
	if ( email_exists( $posted_data['billing_email'] ) ) {
		unset( $posted_data['createaccount'] );
	}

	return $posted_data;
}
add_filter( 'woocommerce_checkout_posted_data', 'flux_remove_createaccount_data_for_known_users' );