Make sure you’re confident and committed to the jump. Maybe you’re tensing up or unconsciously leaning forward etc. If you’re nervous he can’t feel it and may be unwilling to jump!
This is just me, but I would take it back down to basics. The source of the problem is almost always found by going back to the roots. Start off with trot poles, when canter polls, then very small cross rails, and slowly increase the height of jumps. This may take awhile, but it usually allows riders to find the problem and it allows the horse to build confidence. Hope this could help! Good luck!
Work on your legs. Stronger kicks at the right time so the horse keeps on moving.
But first focus on small jumps to build the horse’s courage
Maybe losing confidence- back off larger fences and take him back to simple poles and smaller jumps - also relax the ride 😊
You don’t need to school jumping every day
He may just not enjoy jumping