Shopify Flows - Add Order Line Item Stuck 'Running'

Hey guys, I’m trying to use Flows to detect when an order is received with a certain tag and add a line item to those orders.

The flow is correctly detecting the orders, but is stuck trying to add the line item to the order. I believe I’m using the correct gid format - gid://shopify/ProductVariant/ and flow accepts it with no error, however it doesn’t add the item to the order as expected.

The item is just a £0 empty product set to 100kg to invalidate the WMS from auto-assigning a shipping method for those orders (I know it’s hacky as hell), and it is available on Online Store sales channel.

Any ideas what might be causing the issue? Unfortunately I have no errors to debug.