If you are unable to claim in-game social rewards for being in the Discord server, it is due to your display name and username on Roblox combined being too long.
Your display name and username on Roblox must not exceed 28 characters when combined, as the game checks for your nickname in the format display name (@username)display name (@username), and unless it finds that, the game will not recognize you as being in the Discord server.
To fix this, please change your display name/username on Roblox and make it shorter. When that is done, use /update/update in @709589522555600988 to update your profile.