How to use ACF Forms to manage non ACF controlled meta fields with Advanced Forms Pro.

advanced-forms-pro-prefill-fields-using-custom-data.php

<?php

add_filter( 'af/field/prefill_value', 'prefill_form_field', 10, 4 );

/**
 * @param mixed $value
 * @param array $field
 * @param array $form
 * @param array $args
 *
 * @return string
 */
function prefill_form_field( $value, $field, $form, $args ) {

	// Only run on our desired form.
	if ( $form['key'] !== 'form_5f8f5999245e0' ) {
		return $value;
	}

	// If the user ID can't be determined, bail early and return the original value.
	if ( ! isset( $args['user'] ) or ! is_numeric( $args['user'] ) ) {
		return $value;
	}

	if ( $field['name'] === 'status' ) {
		return get_user_meta( $args['user'], 'membership_status', true );
	}

	return $value;
}

advanced-forms-pro-storing-custom-meta-after-user-edit.php

<?php

add_action( 'af/form/editing/user_updated', 'afp_demo_store_additional_user_meta', 10, 3 );
add_action( 'af/form/editing/user_created', 'afp_demo_store_additional_user_meta', 10, 3 );

/**
 * @param WP_User $user
 * @param array $form
 * @param array $args
 */
function afp_demo_store_additional_user_meta( $user, $form, $args ) {

	// Only run on our desired form.
	if ( $form['key'] !== 'form_5f8f5999245e0' ) {
		return;
	}

	// Get the value from the submission.
	$status = af_get_field( 'status' );

	// If field value could not be retrieved, bail.
	if ( $status === false ) {
		return;
	}

	// Save the value in a custom user meta key.
	update_user_meta( $user->ID, 'membership_status', $status );
}