Facebook Messenger has been updated but this built has for some of the users, I personally faced an issue after upgrading this application. In the screenshot mentioned below you can see that the application my iPhone is connected to a WiFi network but this application is not able to sign-in, infact it shows the error of network.
I restarted the phone and then tried to login again but this also not worked, whereas all the other application (including Facebook app) were working perfectly on my phone. Now I tried to delete this application and then install it again from the App Store, the issue did not get resolved then also. In this post I will tell you the simple solution which can help you to get issue resolved.
To get this problem resolved, try to connect any other WiFi network if you have any nearby (the problem might still persist). If it is still not over then take the help of mobile network to login that application and it will work then, it worked in my case.
This is a small bug and for this you do not have to do anything else, the change the source of the data packet on your phone by just changing the network (whether any other WiFi or Cellular Data). If you have faced any other problem after upgrading this application then please let us know in the comments section.