Idiomatic, Informal To influence or urge by gentle caressing or flattering.
His grin faded a little. "How'd you do it? Sweet-talk one of the guards into letting you in at the head of the line?"1954 November, Mari Wolf, “The Very Secret Agent”, in If:
“Oh, that he finagled. No fate involved. He saw you in the waiting area and sweet-talked the woman behind the counter to sit the two of you together.”2021, Piper Davenport, The Bride Pursued, Sweet edition, Trixie Publishing, Inc.: