Sometimes it's also about building the excitement for training and training at the right time. Do you have him work for any of his meals?
I pick 'foodies' so mine work for kibble. They'd work of pieces of cardboard to boot
Living with Dogs - Canine Coaching
This is kibble. See how at the end, he still wants to PLAY the game. I might do 5 sessions of this with some play in between. Then take a break for an hour, 2 hours, do something similar later. Engage the dog in the training.
start heel - YouTube