Self hosting web x backend not talk to each other

i have a self host at my home, the site work perfect, but i have a problem when i try to connect to my backend api. this API’s it is in another machine, the services web and backend api not talk between them without i expose and make a nat for the backend api machine. web in port 3000 backend por 3600. Anyone have any idea what i do wrong? I don’t want expose my backend!