cannot join server because of internal exception: java.lang.nullpointerexception error

[noob101]

ive tried many, many things on my own and even googling and trying everything. so basically i made a forge server off my pc using a server pack on version 1.16.5 on curse forge and using play.it to use my ip to join it also used "localhost". ive done a server on 1.18.2 using the same method and everything worked fine. but now whenever i start the server trying to join it doesn't work and says "internal exception: java.lang.nullpointerexception". everything starts fine but i cant join when on the mod. here are some of the things i tried using google and my own thoughts:

log in and log out of my account

redownloaded minecraft

deleted forge and downloaded it again

i went to the same version on the normal minecraft launcher and i was able to join it but it didnt have any mods

deleted the world file then creating the world.

also other things but cant think of them all now, since ive been trying for hours and finally decided to ask for help.