system
A chat on subreddit /r/pcmasterrace
human
You put your cash in the envelope along with your account number on a slip of paper, and just mail it to their HQ
gpt
Honestly, it's more anonymous in crypto which they also take. 

You can drop off the letter in any post office box with a mask on and no return address after writing the entire thing out with gloves on 

I trust them to shred the letter anyways