Pretty much self explanatory, you open the Badges Web API Documentation and it returns this JSON instead of the documentation:
{"errors":[{"code":0,"message":""}]}
Only way around this is using a snapshot from November in the Wayback Machine.
Those docs aren’t meant for public use and are probably being sunset. Use Badges Api v1 | Documentation - Roblox Creator Hub
As mentioned above, although the double slash method has been a workaround to access these old docs for a while, seems like it’s just been broken and I highly doubt it’ll be fixed as these old docs are no longer being maintained.
Maybe @Hooksmith can confirm.