Pressing marked-as-shipped return an error ‘Sorry, something has gone wrong’. What usually happens is it clear the screen of the old shipment and creates a new one. my shipment is already in the FBA wharehouse. There is a button that say start-new but I am fearful that it will delete my existing shipment.

Amazon seller support( email snail-mail or phone number) does not appear to exist. I have tried to find it.

https://sellercentral.amazon.co.uk/fba/sendtoamazon/print_labels_step