What type of Betta Pellets are you feeding him? They vary in sizes and some are better than others.
Here are some different types of Betta foods and their sizes for comparison.
This one is anything but "mini", it's the largest brand of Betta pellets on the market and many Bettas have troubles eating it.
Smaller in size and easier to eat.
Everyone here loves these pellets, it's of the "higher end" brand.
My personal favorite, my fish love it and it's what I used to wean my Betta off of flakes.
My least favorite, probably because of the packaging lol, but it's actually fairly healthy for your Betta, roughly the same as the Aqueon brand.
NLS Small Fish Formula, is mainly used for Bettas who are young or suffer from bloating caused by bigger pellets and flakes. NLS (new life spectrum) also makes Betta brand pellets as well, it's the same ingredients as this small fish formula only the pellets are normal sized.
Pellets are better than flakes in all ways. I have a Halfmoon boy who hated pellets but I wanted to wean him off of flakes, or alteast to where he would eat them both. I didn't feed him for 4 days, don't think me cruel or anything, Bettas can live for a month without food and survive (not recommended to try) so a measly 4 days is nothing to worry about and neither is a week.
I soaked the pellet in some tank water, (which many people complain about it losing some or alot of it's nutrients, which is why they like to soak in garlic juice) and then placed a pellet in one at a time, using the Aqueon sized pellets, I fed him one that day and he ate it. The next day I gave him two, soaking them again and the third day I gave him 3, only the first one being soaked. Since then I have been able to feed him pellets without having to soak them at all.
With the average sized pellets you can feed about 5 of them, that's a good number. The Halfmoon which I speak of here gets a little bloated with the normal pellets so I only feed him 3 a day. If you find you Betta being too fat after feedings you can decrease by one until he doesn't look too big. Just remember a little bit of a pudge is okay and normal, you just don't want him to be having trouble swimming or anything.