Hi there,
Conversion Index is just for currencies that are not supported by PayPal so the local currency is converted in PayPal accepted currency.
So for example if Peruvian Sol (unsupported by PayPal) is converted to USD at rate 0.29 then this is the Conversion Index.
However, this feature is not relevant for PayPal accepted currencies as you can receive payments unconverted.
Hope this helps.
Kind regards.
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