I have never seen a Betta with barred flanks. In these cases, I recommend looking at the thumbnails for the genus on Fishbase, so check out Fish Identification.
I would suggest Betta rubra, but your photo doesn't show all the details needed to be definite.
New species of Betta and other related species are still being discovered. Many years ago I met Mr & Mrs Brown who collected the species named after them (Betta brownorum) in a tiny jungle pool created by an elephant's footprint in the mud
