Facebook CEO Mark Zuckerberg called Donald Trump to congratulate him in the days following the Republican presidential candidate’s victory over Hillary Clinton, sources told Buzzfeed News.

During his call to the then president-elect, Zuckerberg congratulated the Trump team on a successful campaign, Buzzfeed reported. The Trump campaign spent millions in advertising revenue on Facebook.

At least three people familiar with the conversation told Buzzfeed that the private call is just one in several endorsements from Facebook of the campaign’s advertising