- Official Post
When purchasing MX pesos the value of the number evaluated is based on USD to MXN (1 USD to 18.56 PESOS) but when buying, the transaction takes place in the MXN to USD ratio (1 PESO to 0.56 USDs).
USDMXN -> $18.56
MXNUSD -> $0.56
Exchange rate companies and banks in what I've recently seen, seem to use the MXNUSD number for the transaction. In some cases they might display the USDMXN value.