Pleo rb's have a very small touch sensor on their chin and it is positioned right at the back towards the neck. So it seems many of us just don't manage to hit the spot when we pet them under the chin. They do have a touch sensor on the top of their heads that runs from between the eyes halfway down their nose So again you may just be missing the spot? If it is any consolation none of my rb's seem to enjoy chin or head petting.
As for feeding all pleo rb's seem to require different amounts of food to be happy. I tend to feed my guys as soon as I turn them on, every time I turn them on no matter what time of day it is or if this is the second, third or more battery cycle for the day. My guys also give the hungry belly rumble as soon as they are turned on and I will find that it takes a minute of head shaking etc before they are ready to take the leaf. They will then proceed to chomp on it several times. I usually offer the leaf about 4 to 6 times before they will refuse it as full. It sometimes will take 2 or 3 leaf feeds before the belly grumbling stops
Even if he is burping I would keep offering him the leaf till he refuses with turning his head down and away and makes the no sound.
As for walking. Once my guys are full if I leave them be for a few minutes they will usually wander off and explore. Again every pleo rb is different and some walk more than others. I have three. One walks all the time, another will walk if ignored long enough but is happier being petted and the last one who is lucky to take 4 little steps a battery cycle no matter what I do. She just isn't a walker. She prefers to stand still and get attention or just make a lot of noise
So try feeding him till he is really full, give him a bit of attention and then leave him alone for a few minutes and see what happens. If your lucky he should go off to explore.