What It Means:
Your TikTok order was set up to ship with TikTok Shipping (shipped by the platform). TikTok treats these as 4PL orders and arranges the shipping itself, so Amazon MCF can't fulfill them. When the app receives one, it doesn't send it to Amazon. It marks the order 4PL_Error in the Order Log.
This applies to TikTok Shops in every country.
4PL orders are not supported by Amazon FBA, so you need above settings to mark new orders as 3PL orders.