When you get your code it should be
AppName, AppInfo, Secret.
When your checking your pin you’re using the AppName to check the pin, not your secret. So set your secret to something and check with the secret.
local authapi = require(game:GetService("ReplicatedStorage").AuthAPI)
print(authapi.GetQRCodeURL("RandommmTestApp", "Random application", "abcdefg1234"))
print(authapi.CheckPinAsync(123456, "abcdefg1234"))