Ok, Mark. My fault, I just thought that "string along" has not the meaning of trick someone.

Thanks France: I asked AI (ChatGPT) in English “I’ll fool him, and give him a taste of his own medicine.” The AI provided some scene context as well:

Context in Le Mariage de Figaro (Act III, Scene 5)

In this scene, Figaro finds himself cornered by the Count’s schemes. The Count suspects Figaro of being in league with the women (Suzanne and the Countess) who are plotting to expose his own infidelities. Figaro, however, is quick-witted: rather than appearing defensive, he turns the situation around by adopting the same duplicity and trickery his adversaries use.

When he says:

« Je l’enfile, et le paye en sa monnaie »

he is essentially declaring that he will beat the Count at his own game.

Phrase unpacked

« Je l’enfile » – “I’ll string him along / I’ll trick him.” The verb enfiler here means to ensnare or dupe, not the modern everyday sense of “to slip on (clothes).” Figaro implies that he’ll catch his adversary in his own trap.

« et le paye en sa monnaie » – “and pay him back in his own coin.” A French idiom meaning to repay someone with the same methods they use — deceit with deceit, cunning with cunning.

Found this - AI:
"Je l'enfile, et le paye en sa monnaie" est une phrase de Figaro dans la pièce de théâtre Le Mariage de Figaro de Beaumarchais, acte III, scène 5, signifiant qu'il va répliquer aux actions de ses adversaires en utilisant leurs propres méthodes, c'est-à-dire qu'il va les tromper ou les déjouer en utilisant leur propre ruse et leur propre malhonnêteté.
Analyse de la phrase

« Je l'enfile »
: Cette expression signifie "je le prends", "je le trompe", "je le subterfuge".
« et le paye en sa monnaie »
: Cela veut dire qu'il va lui rendre la pareille, qu'il va le traiter de la même manière, en utilisant la même tactique ou la même tromperie.