Booking non-USD tx fees

[Eric Altendorf]

I'm trying to model the following transaction: an exchange of USDT for TOKEN (conceptually a "buy"), where the disposal of USDT can register PnL (wrt USD), but also where the exchange charges a fee in either USDT or TOKEN.  The latter bit means the fee is a disposal of USDT or TOKEN (with corresponding additional PnL) and a matching USD leg in the Fees or Commissions account.

I tried modeling it this way which seemed most explicit:

2020-01-01 * "Trade USDT for TOKEN"
  Assets:Exchange:TOKEN      200.00       TOKEN {5.00 USD}
  Assets:Exchange:USDT     -1010.1010101  USDT {} @ 0.99 USD  
  Assets:Exchange:TOKEN       -1.00       TOKEN {} @ 5.00
  Expenses:Financial:Fees      5.00 USD

As a standalone or initial transaction, this doesn't book ("Too many missing numbers for currency group 'USD'").  I guess it's because the -1.00 TOKEN disposal can't match against an acquisition in the same transaction (since here there is no pre existing TOKEN balance).  There are other slight variants of this when I sell, or have preexisting balances.  I could instead:

- Split the two fees legs into a separate subsequent transaction

- Internally collapse and net out the legs on Assets:Exchange:TOKEN

I don't really like either of these a lot because they obfuscate what's "really" going on, but they would work.  Any other suggestions on clear and correct ways to book this?

thanks,

eric