Is it permissible to sell a mortgaged property in Monopoly, and if so, what are the consequences of doing so"?

In Monopoly, it is not permissible to sell a mortgaged property. If a player tries to sell a mortgaged property, they must first pay off the mortgage before selling it. If they sell it without paying off the mortgage, the buyer must immediately pay off the mortgage plus an additional 10 interest.