First of all the suggestion to downgrade your version is a bad suggestion which should never have been given. Especially if it worked before at the beginning... so it is quite logical that downgrading would not be a solution to your problem at all...
What I suggest is to remove your current downgraded version and reinstall the latest one (for your operating system). Note that in the latest version the webcam options aren't there anymore and have been replaced with the video call functions. So you need to select "
start a video call" instead. When people (or you) do select one of the webcam options in an older version of Messenger, then contacts who use the latest version will indeed not see the invitation or get the "
contact has declined" message right away. This is not a bug but "by design" (don't laugh, it is
).
So, in a nutshell: start by reinstalling the latest Messenger version, and take it from there to troubleshoot and fix...
/ 
