That id you are putting in inventory_item_id is not an iventory_item_id but an order_id. Also, your comma is inside the double-quote rather than outside it. This should read like {“location_id”:154example", and NOT {“location_id”:154example,"
Not sure of your use case here, but if you need to update each inventory item in the order, you will need to loop over the lineItems and their inventory items in the action using liquid to build the list of items you want to update.
I’d recommend using Send Admin API request instead and call the inventoryAdjustQuantities mutation, which allows setting multiple quantities at once and should be easier to use than Send HTTP Request. See https://shopify.dev/docs/api/admin-graphql/2024-01/mutations/inventoryAdjustQuantities