Smart Payment Buttons passing custom variable for IPN

Question

I have two Smart button on my website for a monthly subscription (working well). I successfully receive the IPN response with the payment information ready to be added to the Database. But I need to get the UserID of my application with the IPN response.

How can I pass custom variable with my Smart payment button so it can be passed to the IPN (for buying transaction and refund/cancellation ones if possible?)

Here is my Smart button code :

<div id="paypal_button"></div>

<script src="https://www.paypal.com/sdk/js?client-id=[ID]...></script>

<script>
paypal.Buttons({
    style:{
        color:"blue",
        shape:"rect",
        label:"paypal",
        tagline:false
    },
    createSubscription: function(data, actions) {
        return actions.subscription.create({'plan_id': 'P-02S33....'});
    },
    onApprove: function(data, actions) {
        alert('You have successfully created subscription ENTERPRISE' + data.subscriptionID);
    }
}).render('#paypal_button');
</script>

Answer 1

From June 2020 you can pass a custom_id with the paypal subscription button like this:

  createSubscription: function(data, actions) {
    return actions.subscription.create({
      plan_id: "P-1234567897897AAA",
      custom_id: "1344", // for example your internal userid
    });
  },

Now with the webhook (if you use PHP):

// get data from Paypal Webhook POST
$data = json_decode(file_get_contents("php://input"));

error_log('custom_id: '.$data->resource->custom_id);

// also helpful for debugging
error_log(print_r($data, true));

Events that have the custom_id included as described above:

• BILLING.SUBSCRIPTION.CREATED
• BILLING.SUBSCRIPTION.ACTIVATED

For event:

• PAYMENT.SALE.COMPLETED

You need to use:

error_log('custom_id: '.$data->resource->custom);

Without the _id in the end.

Note: I have written a comprehensive tutorial that hopefully will help developers to get things done. Tutorial: How to integrate Paypal Subscription API with PHP and Javascript (2021) - Complete Guide