How can I debug the JSON.parse error when modifying Stripe's checkout_session for email consent?

Below is a summary of what’s happening and some next steps you can take to debug the issue.

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What’s Happening

When you add the 'consent_collection' => ['promotions' => 'auto'] or switch the mode (for example, to “subscription”), the response returned by your server (or passed along by Stripe) no longer follows the expected JSON schema. As a result, when Stripe’s JS code calls JSON.parse() on the response, it fails with a syntax error because it’s either empty or contains unexpected data (often HTML from a 404/500 error).

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How to Inspect the Returned Object

1. Check Your Browser’s Developer Tools (Network Tab):

   • Open your browser’s DevTools (usually by pressing F12) and go to the Network tab.
   • Run your checkout flow and examine the request that your page makes to your backend (or directly to Stripe if you’re using their hosted endpoint).
   • Look at the Response tab to see if you’re getting valid JSON or if there’s an HTML error message, which would give clues such as a 404 (Not Found) or a 500 (Server Error).

2. Log the Response Server-Side and Client-Side:

   • Server-Side (PHP): Before sending the response you could temporarily log the session object you received from Stripe. For example, add something like:

     PHPCopied
     error_log(print_r($session, true));

   • Client-Side (JavaScript): Wrap your JSON parsing logic in a try/catch block to capture and log the error along with the response data:

     JAVASCRIPTCopied
     try {
       JSON.parse(data);
     } catch (error) {
       console.log('Error parsing JSON:', error, data);
     }

   This will allow you to see exactly what’s being received by the JS code.

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Why Changing the Checkout Session Causes the Error

• Schema Mismatch or Missing Required Fields:
  The Checkout Session object has specific requirements for each mode. For example, when switching from one payment mode to another (e.g., from payment to subscription) or adding parameters like consent_collection, the API might expect additional required parameters. If these are missing or if the integration isn’t updated to handle the new configuration, the Checkout Session creation might fail.

• Invalid API Response:
  When the API returns an error (or an HTML page in case of a misconfigured endpoint), Stripe’s JavaScript isn’t getting valid JSON. Once you know what the raw response is (by inspecting the network request and adding logging), you can identify if it’s due to an incorrect URL, invalid/expired API key, or missing required parameters.

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Next Steps

1. Inspect the Network Response:
   Use your browser’s developer tools to check what your server is sending back. Look for indicators of an API error (like an HTML error page).

2. Review Required Parameters for Your Mode:
   If you change the mode (e.g., to “subscription”) or add new optional parameters like consent_collection, double-check the most recent Checkout Sessions API docs to ensure all required parameters are included.

3. Log Details Thoroughly:
   Add both client- and server-side logging to capture the full error response and potentially any error messages coming directly from Stripe.

4. Check Your API Version:
   Make sure your integration (both server-side and client-side) is using the latest supported API version that includes support for email consent collection.

By following these steps, you should be able to pinpoint why the response isn’t valid JSON and adjust your implementation accordingly.

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