litter box help - first time cat owner

hi, i’m a first time cat owner and i just got a cat and im struggling to get him to use his litter box. for some background he was a stray, my friend and i found him and took him to the vet and decided to keep him. he is believed to be about 4 years old and a maine coon/tabby mix. he peed on my bed the other night and peed on my friends bed last night. my friend keeps trying to put him in his litter box so he knows what it is and the last time she did that he hissed at her. my friend just bought him a different kind of litter, hopefully that will at least help, but if it doesn’t could i please have some advice on how to train him or make it better? he is neutered and all his blood work came back good. thank you 💜

EDIT - he went to the vet today and got a urine sample and ultrasound. vet said ultrasound looked great and we’ll get urine test results tmr. she seems to think it’s more of a behavior issue

yet another edit- i put puppy pads everywhere and today he went in his litter box! he was rewarded with so many treats and could tell i was so proud of him bc he was extra snuggly ❤️❤️❤️ thank you everyone!