What led to verbal fight between US' Trump & Ukraine's Zelenskyy?

The verbal fight between US President Donald Trump and Ukraine's Volodymyr Zelenskyy started after VP JD Vance suggested diplomacy with Russia will help Ukraine in the war. Subsequently, Zelenskyy asked Vance what diplomacy was he talking about when no one stopped Vladimir Putin earlier. Vance then accused Zelenskyy of not being thankful, following which Trump rebuked his Ukrainian counterpart.