bro-every roll
Resetting Seed!
Betting 0.0000004 at 48% chance to win, high
Resetting Seed!
Betting 0.0000001 at 48% chance to win, low
Resetting Seed!
What is the nonce value being shown in the bet history?

The screenshot you showed had an incrementing nonce value... if it is always zero (which according to Seuntjie it will be for 999Dice), then this code will attempt to reset the seed (and do nothing anyway) on every single roll.
Just FYI, 999dice uses a new server and client seed combination for every (normal) bet, the nonce will always be 0 for 999dice in DiceBot.
Similarly, calling resetseed on 999dice has no effect, since it's reset for every bet anyway. (to the effect that no request is actually sent to the site when you call resetseed)
and how then to control whether the reset worked or not?
Sounds like you don't need to... as it is reset on every single bet.
If you want to see the values being used so you can make sure that it is actually changing then add these print() calls at the beginning of dobet():
...
function dobet()
print("client: " .. lastBet.clientseed)
print("server: " .. lastBet.serverseed)
-- all your other code goes here
end
You should see the client/server seeds output to the console for every roll and that the client and server seeds are changing every single time.