DeserialisationError when exporting UnbalancedTx

Question

When converting my UnbalancedTx to an ExportTx using the export function, I get this error:

Left (Tag \"toCardanoPolicyId\" (Tag \"1 bytes\" DeserialisationError))

What is very strange is that when I submit the unbalanced transaction with submitUnbalancedTx in the emulator it works and the transaction gets executed. So it should be fine. I feel like this is a bug but I could also be missing something. Before digging deeper, I wanted to post this issue to see if someone can help me. Does anybody see what could be the reason for this issue ?

The error comes probably from function toCardanoMintValue on line 531 here: https://github.com/input-output-hk/plutus-apps/blob/main/plutus-ledger/src/Ledger/Tx/CardanoAPI.hs

The contract that I have looks like this:

buyTokensTx :: forall w s. TokenPool -> BuyTokensParams -> Contract w s Text (Either ToCardanoError ExportTx)
buyTokensTx pool param = do
  m <- findTokenPool pool
  case m of
    Nothing -> do
      logInfo @String $ "no token pool found with nft: " <> show (nft pool)
      return (Left $ TxBodyError "Error: cannot find token pool")
    Just (oref, o, state) -> do
      logInfo @String $ "found token pool with nft: " <> show (nft pool)
      let lookups = ...
      let txc = ...
      case Constraints.mkTx @TokenPool lookups txc of
        Right ut -> do
          let unbalTx = Constraints.adjustUnbalancedTx ut
          return (export def myNetworkId unbalTx)
        Left err -> return (Left $ TxBodyError $ "UnbalancedTx error:" <> show err)

Answer 1

I finally found the issue and I think I might not be the only one to fall into this trap.

What happened is that I defined an asset class that I used as a placeholder for a stable coin in my smart contracts. I chose the following values that I saw in one tutorial:

stableCoinSymbol :: CurrencySymbol
stableCoinSymbol = "ff"

stableCoinTokenName :: TokenName
stableCoinTokenName = "USDT"

I then used this stable coin in the UTxOs of my transactions. Interestingly this works fine in the emulator, but throws a serialisation error (of course) because ff is not a valid CurrencySymbol.

So changing ff to a random valid one (e.g. 8d803516132f6fb8ddfcf168065886bf44ecc9e0023b570963b4bac8) fixed the issue.