Nether wont work/doesnt exist for some reason

so i been playing with my friends a modded server everything was working fine, but one day i tried to enter the nether and it wouldnt let me enter not it was bc of tps it just doesnt work for all players the nether folder was in the server folder, bc we didn't have anything built in the nether i thought i would just try to reset which didnt work... can anyone help?

Quote from AlexanderSniper1

Do you have the Dim-1 file in the world files?

yup, but for some reason it just doesnt allow anyone to enter :/// it just does the nether effect infinitely...

Quote from Julian

Are you sure the nether is enabled in the options?

Ye, the very first thing i thought when it wouldn't let me in was the options checked and it was enabled...

i've also tried to run a excute command to enter the nether says unknown dimension...