Latest Facebook Messenger 204 user agents:

User Agent Platform Device
Mozilla/5.0 (Linux; Android 8.0.0; LLD-L31 Build/HONORLLD-L31; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/75.0.3770.101 Mobile Safari/537.36 [FB_IAB/Orca-Android;FBAV/204.0.0.14.119;] Android 8 Honor 9 Lite
Mozilla/5.0 (Linux; Android 8.0.0; H4113 Build/50.1.A.13.123; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/72.0.3626.105 Mobile Safari/537.36 [FB_IAB/Orca-Android;FBAV/204.0.0.14.119;] Android 8 Xperia XA2 Dual
Mozilla/5.0 (Linux; Android 7.1.1; Moto E (4) Plus Build/NMA26.42-162; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/72.0.3626.105 Mobile Safari/537.36 [FB_IAB/Orca-Android;FBAV/204.0.0.14.119;] Android 7 Moto E4 Plus
Mozilla/5.0 (Linux; Android 6.0; FRD-L04 Build/HUAWEIVAT-L04; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/72.0.3626.121 Mobile Safari/537.36 [FB_IAB/Orca-Android;FBAV/204.0.0.14.119;] Android 6 Honor 8