##You can only either Flurry of Blows or take the unarmed strike from Martial Arts.
You can only either Flurry of Blows or take the unarmed strike from Martial Arts.
Either the additional unarmed strike from Martial Arts or the two strikes granted by Flurry of Blows use a bonus action. (PHB p.78, variously)
But "you can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available to you." (PHB p.189, "Bonus Actions")