Latest Facebook Messenger 138 user agents:

User Agent Platform Device
Mozilla/5.0 (Linux; U; Android 4.3; vi-vn; ASUS_T00J Build/JSS15Q) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 4 ZenFone 5
Mozilla/5.0 (Linux; U; Android 4.3; pt-pt; GT-I9300 Build/JSS15J) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 4 Galaxy S III
Mozilla/5.0 (Linux; U; Android 4.2.2; pt-pt; ME173X Build/JDQ39) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Safari/534.30 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 4 MeMO Pad HD 7
Mozilla/5.0 (Linux; Android 6.0; London Build/MRA58K; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/44.0.2403.119 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 6 London
Mozilla/5.0 (Linux; Android 5.1; Lenovo P1ma40 Build/LMY47D; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/49.0.2623.105 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 5 Vibe P1m
Mozilla/5.0 (Linux; Android 5.1; HUAWEI CUN-L01 Build/HUAWEICUN-L01; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/61.0.3163.98 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 5 Y5II
Mozilla/5.0 (Linux; Android 5.1.1; SM-J500FN Build/LMY48B; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/61.0.3163.98 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 5 Galaxy J5 (2015)
Mozilla/5.0 (Linux; Android 5.1.1; SM-J320F Build/LMY47V; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/61.0.3163.98 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 5 Galaxy J3 (2016)
Mozilla/5.0 (Linux; Android 4.4.2; CHC-U01 Build/HuaweiCHC-U01) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/30.0.0.0 Mobile Safari/537.36 [FB_IAB/MESSENGER;FBAV/138.0.0.20.92;] Android 4 G Play Mini
Mozilla/5.0 (iPhone; CPU iPhone OS 11_0_2 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) Mobile/15A421 [FBAN/MessengerForiOS;FBAV/138.1.0.52.91;FBBV/74882298;FBDV/iPhone6,2;FBMD/iPhone;FBSN/iOS;FBSV/11.0.2;FBSS/2;FBCR/TIM;FBID/phone;FBLC/pt_ iOS 11 iPhone 5S