Discord API - random "invalid code" error passing back generated OAuth2 code - oauth-2.0

Question

I've successfully implemented Discord's OAuth2 flow using the authorization code grant type into my application. The end user navigates to Discord's OAuth2 link for my bot, authorizes its access, and Discord redirects them back to my site with a code querystring. The bot then exchanges this code for an access token by querying Discord's API. Documentation on this process is available here for reference.
However, roughly every 50-100 requests to the exchange endpoint, I receive a 403 with the error invalid_grant and the description Invalid "code" in request. Frankly, I don't understand how the code just provided by Discord's system is instantly invalid. The same user can complete the process again and no error is returned the second time.
Out of desperation, I tried toggling on the option in the Developers Dashboard named Requires OAuth2 Code Grant seeing that it said "if your application requires multiple scopes," but it made no effect. I've also tried endless debugging, but the circumstances under each occurrence are apparently random. Oddly enough, I can't find anyone with the same issue online.
Below is the request I'm making in Node.js using the superagent library. It matches the documentation and works perfectly, other than the response randomly being the error described.
superagent.post('https://discordapp.com/api/v6/oauth2/token')
.type('x-www-form-urlencoded')
.set('Content-Type', 'application/x-www-form-urlencoded')
.send({
client_id: process.env.BOT_ID,
client_secret: process.env.BOT_SECRET,
grant_type: 'authorization_code',
code,
redirect_uri: process.env.OAUTH2_REDIRECT_URI,
scope: 'identify guilds.join',
});
I can confirm that all variables match their expected values. The value of redirect_uri matches that of redirect_uri in the original URL used. code is the value of the code querystring returned through the OAuth2 flow.
What (if anything) am I doing wrong that's causing the error?
Update 1:
Discord has directed me to the API GitHub repo, and I found the issue closed here. Commented and will update here if I receive any helpful info or resolve the issue completely (hopefully the case).

Answer 1

Ran into the same issue using nodejs. Leaving here notes for prosperity:
On Node, if there is no explicit app.head() handler, the .post() handler receives all head requests
Several Android phones, upon being redirected from discord, first send a head request to the endpoint
Meaning:
The user authenticates on discord, then through the redirect back, does a head request. This pulls discord with the code, BUT directly afterwards it also does a post request, which will fail (as you already used the code once), and possibly un-authenticates the user.
Solution for my specific issue was an explicit .head handler for all callback endpoints, which basically just returned the same headers (a redirect) as the post one did, but without calling discord.
Hope this helps.

Answer 2

did you use the OAuth2 link to invite your bot to your server - with the correct permissions? If so, in your main.js file did you define the token?
I.e. bot.login(“YOUR_TOKEN_HERE”)
I would recommend not toggling the ‘Requires OAuth2 Code Grant’ as it is a pain to do anything with in the beginning.
Please let me know of any progress :)