The Red Devils are ready to part with £35 million up front, with another £15 million to come afterwards in add-ons once he reaches certain milestones.
However, the Eagles deem those terms unrealistic for a player who only started playing first-team football 18 months ago.
Palace have told United they must pay £45 million upfront and also review their initial bonuses and add-ons if they wish to finally secure the services of Wan-Bissaka.
Manager Ole Gunnar Solskjaer plans to complete the signing of the 21-year-old as soon as possible as he wants as much of his squad in place by the start of pre-season training on July 1.
The Norwegian sees the Palace star as his ideal first-choice in the position next season, and the Englishman is willing to swap Selhurst Park for Old Trafford, but has been left frustrated as negotiations and fees-haggling between both sides drag on.
Wan-Bissaka is currently on international duty with the under-21’s at the European Championship, and will be hoping to quickly put his horror performance on Tuesday night against France behind him.