They're under the same umbrella, and are functionally the same thing. Bi is just compatibility with the same/different genders, pan is just compatibility with all genders. Bisexual as a term has had a long and confusing history (it essentially meant intersex in the olden days), so then another standard was created (bisexuality as we think of in the contemporary context) as the terminology evolved, then another standard was created on top of that within the last 30ish years or so (pansexuality).

So basically this, lol.

Scientists now just refer to the entire category as "Bi+" as future forks come out. You get to choose which flag you like best, and everyone knows you are on the universal compatibility standard x3