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The song "All In My Head (Flex)" by Fifth Harmony features guest vocals from Fetty Wap. Released in 2016 as the fourth single from their sophomore album "7/27," the track blends pop and R&B genres, with Fetty Wap's distinctive rap verse adding an urban edge to the song. "All In My Head (Flex)" showcases the collaboration between Fifth Harmony and Fetty Wap, resulting in a catchy and vibrant single.