If you receive an email from eBay LINK about a failed order that will not go through to Woocommerce due to Null Payload the first place to check in actual Order itself in eBay LINK.
The email you may have received will look like this
Unfortunately, the order was not able to be received by WooCommerce for the following reason:
Failed to notify retailer for order 192686124514-1559913507009 of retailer Party Buzz. Details: Null payload, couldn't get details?
From Orders, All Orders search for the order. Alternatively there may be an alert on the Dashboard where you can click through to any failed orders. Click to view the full Order Page, on the Order Page under Line Item, under Product in Red it will say No SKU. This means we have imported the order from eBay but eBay LINK cannot match the items SKU to a product.
Points to note.
Have you listed the item manually on eBay, if so you will need to manually full this order in eBay LINK.
We can only push orders to your ecommerce store where we have a product for the item that has been ordered.
You can use the Fulfilled Manually button on the Order Page in eBay LINK.
You may continue to receive alerts about the order, once you set the order in eBay LINK to fulfilled the alerts will stop.
Please also read this FAQ on Retailer Notified Failure order - http://ebaylinksupport.omnivore.com.au/support/solutions/articles/17000042523-what-does-the-order-status-retailer-notified-failure-mean-