Not sure if there is or where there is a tech support forum anymore so I'm posting in general, apologies if incorrect!
Using Steam launcher to join the server I click on server 1, click setup mods, enter the password and A3 loads up. I then get an error message saying some of my .pbo's are not signed by a key accepted by this server. I have had this a bunch of times back in arma2 days, and it was always because I accidentally left unsigned stuff activated when joining. However if you look at the location of the aforementioned .pbo's below, they are actually in a hidden folder (!workshop). I have never seen this setup before. Any ideas? Below is an example location.
"D:\Program Files (x86)\Steam\steamapps\common\Arma 3\!Workshop\@ace\addons\EXAMPLE_NAME_GOES_HERE.PBO