WooCommerce subscriptions missing _pronamic_subscription_id meta

[rvdsteege]

Through a support ticket it came to our attention that there are older WooCommerce subscriptions without the _pronamic_subscription_id meta. This results in:

• payment for a subscription not being linked to the Pronamic subscription;
• the recurring payment will be created for a Mollie customer only, without specifying which mandate to use (if there are multiple valid mandates for a customer, this can lead to using the 'wrong' mandate).

The meta is used to add the subscription to a payment, so that the Mollie mandate ID can be retrieved from the subscription and set correctly on the payment when processing subscription payments:

• https://github.com/pronamic/wp-pronamic-pay-woocommerce/blob/4.1.1/src/Gateway.php#L811
• https://github.com/pronamic/wp-pronamic-pay-woocommerce/blob/4.1.1/src/SubscriptionHelper.php#L33-L48

In a discussion with @remcotolsma, it was suggested to add an upgrade script to add the meta to WooCommerce subscriptions where necessary. This can be done in the following way:

1. loop through Pronamic subscriptions
2. get WooCommerce subscription for subscription source
   (note: source IDs can lead to WooCommerce first orders and subscriptions)
3. add _pronamic_subscription_id meta to WooCommerce subscription (see https://github.com/pronamic/wp-pronamic-pay-woocommerce/blob/4.1.1/src/Gateway.php#L419)

Internal Help Scout ticket: https://secure.helpscout.net/conversation/1949568266/24219