upload base64 encoded image data

[hh]

Moreover it is possible that they expect JSON-Base64 (without saying it).
Then instead of urlencoding the base64 code the following should work.

put base64Encode(myImg) into tImage64
replace numToChar(10) with empty in tImage64 -- doesn't harm
replace "+" with "-" in tImage64
replace "/" with "_" in tImage64
replace "=" with empty in tImage64 (the zero to two trailing "=")
put "\n" after tImage64

[See https://jb64.org/specification/]