Bangle.js App Loader returns "Upload failed, Unexpected response"

easiest to verify flash chip is working is to try to wake it from deep sleep and read ID,
in Web IDE try to paste this line by line

var f=new SPI();f.setup({sck:D19,miso:D20,mosi:D27­,mode:0});
f.send([0xab],D21);//wake spi flash from deep sleep
f.send([0x90,0,0,1,0,0],D21) // get flash id
f.send([0x9f,0,0,0],D21); //get flash id

the last two lines should return something else than just array of zeroes or 255.

hopefully the pinout is right, got it from https://github.com/espruino/Espruino/blo­b/master/boards/BANGLEJS.py#L131

EDIT:
also you may try to toggle reset pin just in case, D17.reset() and D17.set() and set write protect high D31.set()