Trouble Connecting Headphones to FLX-4

Hi Community! I'm having trouble connecting my dj headhphones to my FLX-4 and I don't understand why. The headphones are Pioneer DJ headhpones so there shoulnd't be a compatibility issue. Additoinally, my setting is set to "Master Output -- Master and Headphones Output -- Phones." Can someone help me out? Thank you so much.