give-free.php

<?php
/**
* Plugin Name: Give - Free
**/

/**
 * Register our plugin so it shows up as an option in the Give gateway settings
 */
add_filter( 'give_payment_gateways', function() {
    // Here replace 'give_free' with a unique slug for your plugin.  You will use this slug throughout this plugin.
    $gateways['give_free'] = array(
        'admin_label'    => esc_attr__( 'Free', 'give-free' ),
        'checkout_label' => esc_attr__( 'Free', 'give-free' )
    );
    return $gateways;
} );

/**
 * This action will run the function attached to it when it's time to process the donation submission.
 *
 * Here you use the slug you made above at the end of the action name, give_gateway_YOUR_SLUG
 **/
add_action( 'give_gateway_give_free', function( $purchase_data ) {
    $payment_data = array(
        'price'           => $purchase_data['price'],
        'give_form_title' => $purchase_data['post_data']['give-form-title'],
        'give_form_id'    => intval( $purchase_data['post_data']['give-form-id'] ),
        'give_price_id'   => isset( $purchase_data['post_data']['give-price-id'] ) ? $purchase_data['post_data']['give-price-id'] : '',
        'date'            => $purchase_data['date'],
        'user_email'      => $purchase_data['user_email'],
        'purchase_key'    => $purchase_data['purchase_key'],
        'currency'        => give_get_currency(),
        'user_info'       => $purchase_data['user_info'],
        'status'          => 'pending', /** THIS MUST BE SET TO PENDING TO AVOID PHP WARNINGS */
        'gateway'         => 'give_free' /** USE YOUR SLUG AGAIN HERE */
    );

    /**
     * Here you will reach out to whatever payment processor you are building for and record a successful payment
     *
     * If it's not correct, make $payment false and attach errors
     */

    // record the payment which is super important so you have the proper records in the Give administration
    $payment = give_insert_payment( $payment_data );

    if ( $payment ) {
        give_update_payment_status( $payment, 'publish' ); /** This line will finalize the donation, you can run some other verification function if you want before setting to publish */
        give_send_to_success_page();
    } else {
        // if errors are present, send the user back to the donation form so they can be corrected
        give_send_back_to_checkout( '?payment-mode=' . $purchase_data['post_data']['give-gateway'] );
    }
} );