I suppose your address starts with a "bc1"? If so, you'll have to create a legacy wallet first because it appears that Coinfloor doesn't support bech32 addresses.

IIRC, it's no longer possible to create legacy wallets with the UI after the last electrum update so you'll have to do it using the command line. See this: https://www.reddit.com/r/Electrum/comments/mku14h/how_do_you_create_legacy_wallet_from_command_line/