... then I rewrote my code with my newfound knowledge, only to discover it won't work!
<headbanging />
I discovered it's some kind of capitalization issue. parameter names in a fetch are sensitive to their first letter's case. but not to the case of other letters.
e.g. CurrencySymbol != currencySymbol
but currencySymbol == cUrrENCYSymbol == cURRENCYSYMBOL.
I have been browsing the documentation but didn't find anything mentioning it (except for case-sensitiveness of $variables).