I have found with some of the buns we have got, you can tell which had a lot of hay and which havent,
Some days they will empty their hay racks, some days it looks barely touched,
Do you use a hay rack?
Maybe he is eating, but not a lot?
He is relitively new, so will still be settling in,
What type of hay are you feeding? (eg P@H timothy?)
Maybe its just different to what he is used to, I get bales of hay, the quality varies, and each bun has different tastes, some prefer the lower quality and stick their nose up at the richest smelling greenest hay, and others are the other way round, and some will eat anything lol
Maybe get a different bag of hay from somewhere else (someone on here could maybe point you in the right direction as I have no clue when it comes to bagged hay from stores)
Hope he starts munching soon
Edited to add - Please be careful giving greens to him at this age, small amounts and not very often, his tummy will still be adjusting to food, and can be very delicate, so may be best to cut these out for now?