Executives at Discovery, wary of antitrust rules, were constrained from advising their counterparts at CNN until the merger was done. CNN+ had lost its champion when Mr. Zucker left in February because of an undisclosed romantic relationship with a colleague. But Jason Kilar, the WarnerMedia chief executive, forged ahead anyway, launching the streaming platform on March 29 to the frustration of the Discovery leadership.

It quickly became apparent that Mr. Zaslav had a very different view on digital strategy.

On the morning of April 11, the first business day of Discovery’s ownership — and 90 minutes before its WBD stock even went live on Nasdaq — JB Perrette, Discovery’s global head of streaming, convened a meeting with CNN executives.

Mr. Perrette had a message: Marketing of CNN+ was to be suspended, pending a formal review of the business, three people familiar with the conversation said.

Executives at Warner Bros. Discovery wanted to merge its other subscription platforms — Discovery+ and HBO Max — into one giant streaming service. They were not convinced that a niche product like CNN+ could be viable on its own.

And there was the matter of the debt. Discovery’s merger left the conglomerate owing about $55 billion, which executives are now under pressure to repay. CNN had been planning to spend more than $1 billion on CNN+ over four years, two people familiar with the matter said, even renting out an additional floor of its pricey Manhattan skyscraper.

Andrew Morse, CNN’s chief digital officer and a key architect of CNN+, who became the biggest internal champion of the service, countered that subscription-based online news could be successful, citing The New York Times as an example. Executives at CNN+ said they had secured 150,000 paying subscribers and were on a pace to hit first-year subscription goals.

Executives at Discovery were not impressed: At any given time, fewer than 10,000 people were watching the service, said two people familiar with the numbers, who were not authorized to speak publicly. (On Thursday, Mr. Morse said he was leaving the network entirely.)