Hey there,
I wasn’t sure if there was a mod/plugin already (I looked everywhere with numerous different Google searches) that basically if the player is using your mod pack when they log in to your server, they will get a reward (either one time or daily, haven’t thought it out much yet). If they’re not using your mod pack, then they will not receive any rewards whatsoever. This may seem odd, but this would primarily be for Pixelmon, where there’s a bunch of different mod packs for various different servers.
If you have any questions/comments/concerns, please feel free to reply! If there is a mod/plugin that already has these features or most of them, then I apologize and ask if you could link me to it.
Thank you for reading, and have a wonderful day.