Shopify has removed the checkout_id from the checkout and order webhooks. Consequently, the checkout_id field is removed from the metadata and is no longer mapped for these module events:

• Order creation
• Order update
• Order cancellation
• Order fulfillment
• Order partial fulfillment
• Order payment

You are advised to update your infrastructure and webhook handlers. To know more, See Removed Checkout ID from checkout and order webhooks - Shopify developer changelog.