Yeah, I'd only say the same thing to you as I did in that other OAuth thread which is I don't see this as a Let's Encrypt issue.
If you are following specs or instructions I would contact them for suggestions. Your messages are not as clear that it is a problem connecting to discord but that is still a fair guess.
You just have some routine program debugging to isolate the exact HTTPS request that is failing and correct the cause. It is well outside the scope of this forum. Perhaps even a general programming forum is helpful (stackoverflow even)
My only tip is to look at this file and make sure it is a valid CA root store for the app stack you are using.