Rejecting someone kindly feels uncomfortable, but it is far kinder than silence, which leaves the other person waiting and assuming the worst.

Be clear rather than vague. Saying you are just busy invites them to wait, while saying you did not feel a romantic connection closes the loop honestly.

Keep the message short: thank them, state the lack of connection, and wish them well. Two or three sentences are enough, and promptness matters.

You do not owe a detailed critique or an endless debate. A calm restatement is a complete answer, and ghosting after real dates is the option to avoid.