Latest Facebook Messenger 115 user agents:

User Agent Platform Device
Mozilla/5.0 (Linux; Android 6.0.1; Redmi 3S Build/MMB29M; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/55.0.2883.91 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/115.0.0.22.69;] Android 6 Redmi 3S
Mozilla/5.0 (Linux; Android 5.0.2; SM-G360F Build/LRX22G; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/55.0.2883.91 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/115.0.0.22.69;] Android 5 Galaxy Core Prime
Mozilla/5.0 (Linux; Android 4.4.4; Y635-L21 Build/HuaweiY635-L21) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/33.0.0.0 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/115.0.0.22.69;] Android 4 Y635 Dual SIM
Mozilla/5.0 (Linux; Android 4.4.2; HTC D816h Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/30.0.0.0 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/115.0.0.22.69;] Android 4 D816h