V4.21 board will not flash

Uploading .pio\build\V421\module_fw_V421_attiny841_421_eF4_hD6_l62.hex

avrdude: error: program enable: target doesn’t answer. 1
avrdude: initialization failed, rc=-1
Double check connections and try again, or use -F to override
this check.

I have a usbasp device which is showing as good in device manager and is being recognised in platformio in vscode, I have triple checked the six wires that go from the icsp headers and when i attempt upload it give the message shown above. any advices would be appreciated. thanks. I get one green flash on the 4.21 slave board when the upload is attempted.

Fixed. Found the -b16 in the general env section and that made the usbasp work. Was adding into env400 mistakenly as i didnt realise at the time the upload flags were board specific or general.