I did not name anything wrong
Of course you have. The .cfg file you posted was named G-EUPJ.cfg instead of GSX-G-EUPJ.cfg, that's why I asked if the file you posted was the one you use. If it is, no wonder it doesn't work, because the name is wrong.
as I simply didn't do anything after installing the airframe and livery.
"not doing anything" will cause exactly this.
There's no automated way to create an airframe-specific .cfg file, you must create one yourself, and in the last screenshot you posted, you ONE had a GSX.CFG, so you don't have the airframe-specific .cfg file you posted (regardless how it was named)
Here is the path I am talking about (C:\Users\mytre\AppData\Roaming\Virtuali\Airplanes\FSLabs A319 IAE) and you can find the file attached below.
Which is, again, wrongly named. The file you posted is called:
GSX-G-EUPJ.cfg.cfg
When it should be:
GSX-G-EUPJ.cfg
And the other two files you posted are wrong as well, since they are both missing GSX- in front of their name. I think what is confusing you, is that from your screenshot of the folder (which contained ONLY a GSX.CFG file and nothing else, no airframe-specific file was there), you have the file extensions hidden in Windows Explorer, and that makes it more difficult to realize at a first glance the complete file name. If you disable that option, it will be easier to realize how a file is really named.
I will attach the Airframe config file (G-EUPJ.cfg) from the FsLabs folder (C:\Users\mytre\Documents\Prepar3D v5 Add-ons\FSLabs\SimObjects\Airplanes\FSLabs A319 IAE\Airframe Configs). I will also send you a fully functioning ariframe config (OE-LKD.cfg) if that helps.
If you keep posting files wrongly named, it's not really helping, because I cannot possibly know if they are still wrongly named in your %APPDATA% folder, or you wrongly named just for posting. If they are like that in the sim, no wonder they don't work.