Mst: Wishlist + Marketing flow

I have been a client for over a year - my customers have been adding items to their wishlist all this time for my 1 and only winter sale - they come to use them today and the app is down. Their lists are gone and no way of creating a new one - error message is - "There was an error in the third-party application."

I can not see anything my end other than an error message.

Really concerned as the sale starts in 9 hours ... have contact developers