Update field in Gravity Forms entry with IBAN on successful payment with Pronamic Pay.

functions.php

<?php

/**
 * Gravity Forms iDEAL fulfillment hook.
 *
 * @link https://github.com/wp-pay-extensions/gravityforms/blob/2.1.2/src/Extension.php#L729-L730
 *
 * @param array                                                   $entry Gravity Forms entry.
 * @param \Pronamic\WordPress\Pay\Extensions\GravityForms\PayFeed $feed  Payment feed.
 */
function gform_ideal_fulfillment_update_entry( $entry, $feed ) {
	// Set form and field ID to update.
	$form_id    = '2';
	$field_id   = '26';

	// Do we want to update this form?
	if ( $form_id !== $entry['form_id'] ) {
		return;
	}

	// Get Pronamic payment.
	$payment_id = gform_get_meta( $entry['id'], 'pronamic_payment_id' );

	$payment = get_pronamic_payment( $payment_id );

	// Get IBAN...
	$iban = $payment->get_meta( 'consumer_iban' );

	// ...or account number.
	if ( empty( $iban ) ) {
		$iban = $payment->get_meta( 'consumer_account_number' );
	}

	// Set IBAN as entry field value.
	$entry[ $field_id ] = $iban;

	// Update the Gravity Forms entry.
	GFAPI::update_entry( $entry );
}

add_action( 'gform_ideal_fulfillment', 'gform_ideal_fulfillment_update_entry', 10, 2 );