A token failed validation: empty, shorter than 50 characters, or missing the two dot separators every Discord token has.
Usually a stray quote, whitespace, a copy-paste truncation, or a placeholder left in .env. The validation rejects any token that does not contain exactly two dot characters.
Open .env and inspect the offending token (the log prints its first 15 chars). Remove surrounding quotes only if python-dotenv isn't stripping them, kill stray spaces and newlines, then re-copy the full token from Discord making sure it contains exactly two dots.
TOKENS="abc123 channel"
TOKENS="MTIzNDU2Nzg5.token_part_2.signature channel_id"