you cannot FILETOSTR the Hindi file, because you get garbage - VFP does not support UTF-8
That's a common misconception about what constitutes the problem and what not. While VFP itself wil always interpret the bytes you load from a file as ANSI - in its currently configured codepage, the bytes are the exact bytes of a UTF8 string and you can forward them in a request URL or body without the need to convert them with STRCONV.
So VFP is only incapable to display UTF-8, STRCONV can be used to convert as much of a UTF8 string into ANSI characters as much characters are also available within the limited 256 character codepage, but that does not mean you can't forward UTF8 to an API endpoint, the FILETOSTR() function does not convert from the file content to ANSI, it will read bytes 1:1 and not convert anything and you also only need to convert yourself with STRCONV, if you want to get the ANSI representation as good as ANSI can represent the given UTF8.
What can hinder the 1:1 transport of bytes is the usage of COM objects and the automatic conversions involved in using COM, but how that is handled is under your control, too, and in usual cases you don't need to care for that. One commonly known way to hinder any autoconversion when traversing from VFP to a COM object is to use binstring=CREATEBINARY(vfpstring). The resulting binstring variable has the same bytes, but when passing it as a parameter to a COM object or setting a COM object property to it, automatic conversions from ANSI to the encoding asssociated with COM are not done.
Also see
CREATEBINARY() is not necessary at all times, but can't harm, as it does nothing to the actual bytes, the display just changes to a hex string, but only within VFP, the length of a binary string is the same as the original and the byte composition, too.
So the only problem you have in VFP is entering a UTF8 string to forwarding it to an API. If you have a UTF8 string, that's good to go, even though VFGP won't display it correctly.
So the major problem VFP has is displaying other encodings, not reading, storing or forwarding them.
Chriss