I probably did something wrong (seeing how I have no experience with this and I have no skill in doing something like this) but Idk what I did wrong
I assume that you have examined this? https://wiki.beamng.com/License_plate_tutorial At a glance I see that you've got some sloppy stuff like mixing up / and \. I'd be sure to get that stuff right. username_mod etc - this is your username, eg "y4123" not the word "username" and "mod" isn't the word "mod" but rather the name of your mod. Please review the tutorial again armed with that knowledge.
You seem to have messed up in the filenames : - Your path is not the same as the path in the tutorial ; yours is "Vehicles\Common\License Plates\Y4123_Spectacular_Peninsulas", but it should be "vehicles/common/licenseplates/Y4123_Spectacular_Peninsulas/". First, it's not the same as the one specified but most importantly, I advise you to never use spaces or accents when modding, they often cause problems - Don't forget to rename every word that points to your username with your username, you still have wrong filenames - You still have messed up in the filepaths, double check the filepaths you edited in the json and the jbeam and compare them to the actual filepath, you should find the problems
here it's because you named your folders Vehicles instead of vehicles and Common instead of common, and now it work