After uploading both rp and dp packs to their respective folders as .zips and unzipped, reloading datapacks in-game results in the message "Custom Music Discs v1.9 by link2_thepast" regardless of what the actual pack name is. /give commands for both individual discs and for all discs result in "Unknown function ". Same result in singleplayer and multiplayer in which the datapack is uploaded to the server.

The title will always be "Custom Music Discs"; the name setting is mostly for internal use to avoid namespace collisions.

Looks like the datapack is referring to custom_music_discs functions, which of course don't exist because you changed the name. I don't see how this could happen in the code... try regenerating your packs and see if that fixes the issue.

Update: I tried running the functions on Vanilla instead of my Forge client, which worked. I then reinstalled Forge and tried it again and it worked. I think the issue was the name of the pack -- when I would it tab before, it wouldn't prompt anything at all, but when I did it after, it had the disc commands available.