The English spelling is traditionally Macao (an archaic Portuguese spelling) and the modern Portuguese Macau. An official webpage on the China Daily website briefly explains this: China City Information-Macao, Macau.
What is the correct spelling: Macau or Macao? - Quora
https://www.quora.com/What-is-the-correct-spelling-Macau-or-Macao
source: 
thank you freedomshift, so both are actually correct