Error: options.uri is a required argument
You need to provide URL information while making a request, check to see that correct URL is getting assigned to your webhook variable, i.e
var webhook = process.env.DISCORD_WEBHOOK;//webhook should be assigned a valid URL for example: 'https://stackoverflow.com/'
try console.log(webhook);
to find out URL for which you are making a request.
Object request has parameter uri not url.https://github.com/request/request#multipartrelated
request({ method: 'POST', uri: webhook, json: { "content": req.body.msg, "username": "Potato" }});