Not directly with the plugin, but for that you can use the function From common events. You could make items that say: "Unlock Character X" and when you get that item a common event is launched that unlocks the character you want.
Hello.
I do not offer support through Discord. I only offer support via email.
Here you have all the information:
https://maxii1996.github.io/Undermax-OnlineServices/undermax/support.html
If you wish to contact me, please fill out the form there!
Best regards.