I know there is a way to check if a player had a player badge however I dont know about roblox badges. Looking at the badge api I dont see anything about roblox badges.
This is 100% possible, games like Roblox Highschool have used this to transfer data from the old game to the new one, I do not know how it’s done, but it is possible
I know that it is possible to check for badge ownership on any badge in the inventory. This includes Roblox badges. You just have to check for a badge with the rblxasset.id that the one of Roblox badges have with the badge API and have an event trigger depending on which badges you have.
Recently I thought, why can’t I just see what endpoints are being used on roblox itself, the website?!? So I went to my profile and inspected element, went to network, went through all the endpoints and found this golden gem: