What am I doing wrong with potty training

I have a 14 weeks old pup that I have had for about 6 weeks now. He is really smart but we are still struggling with potty training. It started by him using his bed to go potty and when out of his playpen my carpet. I have washed the bed so many times already and figured out it works best when he doesn’t have it in there. Right now, he is doing really good in his pen, almost no accidents there, even over night he holds it in for about 8 hours which I’m thrilled about or when I am out of the house for 3-4 hours no problem. However, when he is out of his pen inside the house and I am home, he pees or poops on my carpet. He won’t let me know either even though he knows he has to go outside because as soon as I see him peeing/pooping and shout “no” he runs to the door. I take him out frequently when I’m home. Like today we went out to potty, he peed, then I leave him out there for longer to play/sniff to see if he’ll poop too and he won’t. Then we go inside and he poops on the carpet within 20 minutes. I don’t know if maybe communication is the problem. I have tried the door bell but he didn’t really get it he just torn it off thinking it’s a toy. Maybe I should try again and be persistent? I know he’s smart so what am I doing wrong?