Mayday will look up transactions in the sources base currency.
For example, Mayday HQ’s base currency is £, therefore a bill posted to Mayday HQ in $ will come through to Mayday as the amount converted into £ and posted to the general ledger.
Where does your currency conversion for postings come from?
By default, we use the exchange rate provided by European Central Bank Exchange, but you can override this.
If your Xero organisations do not support multi-currency, and the two entities are not of the same base currency, then the Postings page will force you to post journals in each entity's home currency.