It looks like there was an error.

{
    "error": "invalid_request",
    "error_description": "Missing parameter: \"code\" is required"
}

If for whatever reason you no longer wish for Commix Digital to have access to your Lightspeed account, simply log in to your Lightspeed account, navigate to Settings > Client API Access choose Commix Digital and click remove access.

Warning! Removing access will break your integration!