Twitter CEO Elon Musk hit back at Stephen King after the author challenged him to donate to Ukraine and complained about having a “blue check” on the platform despite not having purchased one.

“I think Mr. Musk should give my blue check to charity,” King tweeted. “I recommend the Prytula Foundation, which provides lifesaving services in Ukraine. It’s only $8, so perhaps Mr. Musk could add a bit more.”

King’s tweet to Musk came after he claimed that he retained his blue check even without subscribing to the platform’s blue check service, which now costs $8 per month. “My Twitter account says I’ve subscribed to Twitter Blue,” King said. “I haven’t. My Twitter account says I’ve given a phone number. I haven’t.”

Musk replied to King’s Ukraine post directly, tweeting, “I’ve donated $100M to Ukraine, how much have you donated?”

Musk went on to mention how his SpaceX organization has taken a financial hit by continuing to fund its Starlink service in Ukraine despite declining money from the Department of Defense.

The company has been paying for terminals, new satellites, satellite launches and satellite maintenance in Ukraine, according to Teslarati.

Twitter removed its legacy verification badges from users’ accounts last week, causing many journalists, actors and other notable figures such former President Donald Trump to lose their verification.

Individuals and businesses, regardless of how prominent, will no longer have a blue check mark unless they subscribe. Still, some celebrities have retained the check mark but said publicly they haven’t subscribed.

Fox News’ Joe Silverstein contributed to this report.