darkSpyro

my cat is around 10 years old and for most of his life he's gone to the bathroom outside. when we first got him he was litter box trained (he wasn't my cat originally) but then he just started going outside so it was fine. whenever he wanted out he'd just go to the door.
now he won't go to the door. we HAVE a litterbox for him but he thinks the floor is a better place to do his business. he usually does it when im sleeping or when i'm at school so it's hard to catch him in the act.

i don't know how to litterbox train him. he absolutely refuses to go inside the box. like, he won't, i bribed him with treats, milk, and food but he won't go in. if i pick him up and put him in he'll frantically try to get out. i switched to different types of litter but it didn't work.

someone pls help me idk what to do. he reallyy needs to learn, especially with the weather getting colder because then he's going to be inside more. help