Betta Fish: Sex identification in short finned bettas

I bought two bettas today for two different tanks since my last boi went over the rainbow bridge after 3 nice years (no signs of disease only signs of senescence- 4weeks of fish-less cycle and water changes nevertheless ) and the other tank was just shrimps and I felt like the population could handle one mouth to feed.
Now the curious thing is that one fish was sold to me as a male and the other one as a female- to me they look absolutely identical from their physical appearance. The koi type is supposed to be a female and the samurai is supposed to be male. My last fish looked similar and was labeled male but didn’t build foam nests- I prefer short fins because I want them to be able to swim well until old age. So now I’m wondering if they are all male, all female or I’m just unable to tell? I let them see each other to show how similar they are behaving- they aren’t moving in together