cedws
commented
5 years ago I've confirmed that it is not possible to delete messages from servers that the user has left. They will show up in the data archives, but the API will return a 403 Forbidden upon attempting to delete them. This means that the script can't delete full message history as it was designed. I don't think there's a way around this unfortunately. Partial deletion will still be able to clear messages from private conversations and servers the user currently participates in.
See https://github.com/c-edw/discord-delete/issues/10#issuecomment-488161706. Full deletion doesn't seem to work as expected. If the script attempts to delete messages from a server the user no longer participates in, it will receive a 403 Forbidden error. I believe this worked in the past but I'm not 100%. I might have introduced a bug, or perhaps Discord changed their API. If they have, I can try to find another way of implementing full deletion.