Repost from stackoverflow:

So I've been at my wits' end for quite some time regarding #[pallet::error] showing up on Polkadot JS apps interface when calling a fallible function from sudo. So as I've come to understand following substrate kitties tutorial that we require to return a DispatchResult out of our dispatchable calls and after doing so, I have a case where I am not seeing any errors on my apps interface, although the operation does fail successfully as I don't see any mistakes on the balancesToAccount hashmap.

This code compiles fine.

    impl<T: Config> Pallet<T> {
        #[pallet::weight(10_000 + T::DbWeight::get().writes(1))]
        /// Allow only Root to mint new tokens & transfer it to some benefactor account
        /// Set a hard uppper limit on the total number of tokens in supply
        pub fn mint(
            origin: OriginFor<T>,
            #[pallet::compact] amount: <T as Config>::Balance,
            benefactor: T::AccountId,
        ) -> DispatchResult {
            // Check if sudo call

            // Check if existing amount doesn't overflow MaxTokenSupply
Error   |---->  Self::does_adding_overflow_maxtokensupply(amount)?;
            // Check if Benefactor already has funds
            let previous_balance = <BalanceToAccount<T>>::try_get(&benefactor).unwrap_or_default();
            let final_balance = previous_balance.saturating_add(amount);
            <BalanceToAccount<T>>::insert(&benefactor, final_balance);

As you can see I have a helper function that will check if minting amount causes a overflow to the total token supply. And that function is defined here:

impl<T: Config> Pallet<T> {
        fn does_adding_overflow_maxtokensupply(amount: T::Balance) -> Result<(), Error<T>> {
            let total_already_minted: T::Balance = BalanceToAccount::<T>::iter_values().sum();
            let new_supply =
            if new_supply <= T::MaxTokenSupply::get() {
            } else {

I was expected ? to automagically cast the Error into something DispatchResult can work with, but I'm not sure if that's happening on this line:


Here's what Polkadot JS apps shows when I give it a number greater than max supply : enter image description here Next I check whether that balance went through (It shouldn't), and indeed it didn't go through. Alice's Balance not updated

What I would like the apps interface is to show an error rejecting such requests as it does in case of BadOrigin. How can I achieve this?

Edit #1: I should mention that this function is only callable by sudo, if that makes a difference. I can see extrinsic Errors on other functions, except this one.

  • @NukeManDan there done. have fun. Commented Feb 9, 2022 at 17:12

1 Answer 1


I'm afraid at the moment the UI does not show these errors. This seems to be a UX fail but I am hopeful that we can fix it. This is the issue to watch:


(The sudo call is successfully invoking the parameter so it is a successful extrinsic even if there are inner errors - same woes with utils.batch, incomplete xcm messages etc.)

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