Cot bed transition

Looking for tips or advice, is anyone's little one in a cot bed/bed? We've transitioned our wee boy to the cot bed and the first three nights we just said night night and left and he went to sleep (just as he did when he was in his cot) but the last few nights he just runs to his bedroom door banging, screaming and crying til one of us goes in and it just continues til I end up going in and stroking his hair til he falls asleep. It takes about 45mins from getting him in bed til he falls asleep. Any advice on how we can get him into bed, stay in bed with no upset?🥺 he has a comforter, temp is perfect, he has a starlight projector with gentle lullaby - all things he's had from day dot. We also read a story or two when we put him to bed.