Building a Dependent Plugin for Split Order Payment

How to extend Split Order Payment from a separate plugin — add your own settings tab, change field requirements, and hook into every notification moment — without editing a single line of this plugin’s code.

1. Detecting the plugin is active

Check for the base plugin before registering any of your hooks, so your plugin degrades gracefully if it’s ever deactivated:

if ( defined( 'CSWC_SPLIT_ORDER_PAYMENTS_VERSION' ) ) {
    // Safe to register the hooks below.
}

2. Adding a settings tab

The Split Settings page (admin.php?page=split-order-payment) builds its tabs entirely from a filter, and renders each tab’s content entirely from an action. The base plugin’s own four tabs register through this exact same mechanism — your tab is a peer, not a bolt-on.

add_filter( 'cswc_split_payment_settings_tabs', function ( $tabs ) {
    $tabs['whatsapp'] = array(
        'label' => __( 'WhatsApp', 'my-whatsapp-addon' ),
        'icon'  => 'dashicons-format-chat',
    );
    return $tabs;
} );

add_action( 'cswc_split_payment_settings_tab_whatsapp', function () { ?>
    <table class="form-table">
        <tr>
            <th><?php esc_html_e( 'WhatsApp API Token', 'my-whatsapp-addon' ); ?></th>
            <td>
                <input type="text" name="whatsapp_api_token"
                       value="<?php echo esc_attr( get_option( 'whatsapp_api_token' ) ); ?>" class="regular-text">
            </td>
        </tr>
    </table>
<?php } );

add_action( 'admin_init', function () {
    register_setting( 'split_order_payment_settings', 'whatsapp_api_token' );
} );

3. Making the participant phone number required

The phone field on the participant form is optional by default. One filter makes it required everywhere it matters — the field’s own label, the frontend JS validation, and a server-side check when the form is submitted:

add_filter( 'cswc_split_payment_phone_required', '__return_true' );

add_filter( 'cswc_split_payment_phone_required', function ( $required ) {
    return (bool) get_option( 'whatsapp_api_token' );
} );

4. Hooking into notification events

You don’t need a new hook to fire alongside the base plugin’s emails — it already fires a plain do_action() at every lifecycle moment, which is exactly what its own email classes listen to. Hook the same actions to send a WhatsApp message (or anything else) at the same moment:

Example — send a WhatsApp reminder alongside the existing email reminder:

add_action( 'cswc_split_reminder_email', function ( $order, $email_id, $row ) {
    if ( empty( $row->access_token ) ) {
        return;
    }
    $pay_url = add_query_arg( array(
        'split-order'   => $row->order_id,
        'split_pay_for' => rawurlencode( $email_id ),
    ), site_url( '/' ) );

    // send_whatsapp_message() is your own integration's function.
    send_whatsapp_message( $row->email_id, sprintf(
        __( 'Reminder: you still owe %1$s for order #%2$d. Pay here: %3$s', 'my-whatsapp-addon' ),
        wc_price( $row->share_amount ), $row->order_id, $pay_url
    ) );
}, 10, 3 );

5. Reading participant data

The tracking table — your primary source

Every participant, on every split, has one row in {$wpdb->prefix}cr_split_order_payments. This is the cleanest structured source for a per-participant integration:

global $wpdb;
$participants = $wpdb->get_results( $wpdb->prepare(
    "SELECT * FROM {$wpdb->prefix}cr_split_order_payments WHERE order_id = %d",
    $parent_order_id
) );

Order meta — the raw split configuration

The parent order also carries the split’s original configuration as a single meta value, useful for the organiser’s chosen split mode or the phone numbers entered at split time:

// Always via the order object — never get_post_meta()/update_post_meta(),
// which silently break under HPOS (High-Performance Order Storage).
$order  = wc_get_order( $order_id );
$split  = $order->get_meta( '_split_order_data' );
$phones = $split['invitee_mobiles'] ?? array();

6. Best practices

• Never touch order data with get_post_meta()/update_post_meta(). Always go through $order->get_meta() / update_meta_data() / save() — raw postmeta calls silently fail once HPOS is active.
• Don’t edit any file inside the base plugin. Every extension point you need is one of the hooks above; a direct patch won’t survive an update.
• Prefix your own option names (e.g. whatsapp_) to avoid colliding with the base plugin’s own settings, which live in the same split_order_payment_settings group.
• Sanitize and escape exactly as you would anywhere else in WordPress — register_setting() accepts a sanitize_callback, and none of this plugin’s hooks sanitize your data for you.

7. Full worked example

A minimal, complete companion plugin putting all of the above together:

<?php
/**
 * Plugin Name: Split Payment — WhatsApp Notifications
 * Description: Sends WhatsApp reminders for Split Order Payment participants.
 * Requires Plugins: woocommerce-split-order-payments
 */

if ( ! defined( 'CSWC_SPLIT_ORDER_PAYMENTS_VERSION' ) ) {
    return; // Base plugin isn't active.
}

// 1. Add our own settings tab.
add_filter( 'cswc_split_payment_settings_tabs', function ( $tabs ) {
    $tabs['whatsapp'] = array( 'label' => 'WhatsApp', 'icon' => 'dashicons-format-chat' );
    return $tabs;
} );
add_action( 'cswc_split_payment_settings_tab_whatsapp', function () { ?>
    <table class="form-table"><tr>
        <th>WhatsApp API Token</th>
        <td><input type="text" name="whatsapp_api_token"
            value="<?php echo esc_attr( get_option( 'whatsapp_api_token' ) ); ?>" class="regular-text"></td>
    </tr></table>
<?php } );
add_action( 'admin_init', function () {
    register_setting( 'split_order_payment_settings', 'whatsapp_api_token' );
} );

// 2. Require a phone number once we're configured.
add_filter( 'cswc_split_payment_phone_required', function ( $required ) {
    return (bool) get_option( 'whatsapp_api_token' );
} );

// 3. Send a WhatsApp message alongside every reminder email.
add_action( 'cswc_split_reminder_email', function ( $order, $email_id, $row ) {
    if ( ! get_option( 'whatsapp_api_token' ) ) {
        return;
    }
    // ...call your WhatsApp API here, using $row->share_amount, $row->order_id, etc.
}, 10, 3 );