Amazon want any MFN item to be converted to FBA item when you want to send it to Amazon Warehouse for FBA fulfilment. ScanPower doesn't automatically convert the MFN items into FBA items while you add the item into Prep & Ship Batch. This is to avoid any accidentally initiated conversion from MFN to FBA.
You can manually convert the MFN listing to FBA listings either in Seller Central or in ScanPower.
Please refer to the below article to convert the MFN item to FBA item in ScanPower.