Last March, Twitter released a survey that hinted at its plans to create a paid subscription service that provides an enhanced user experience with extra tools and analytics.
For now, the closed beta is only available to invited accounts.
The subscription would essentially be for an ad program that would automatically promote posts, up to 10 per day in addition to running month-long Promoted Account ads.
That means a business would pay Twitter $99 per month to pick and choose which of its tweets to promote.
Twitter's advertising products already allow users and business to pay to promote their tweets to a broader audience.
"This program will do the heavy lifting", Twitter wrote on its website. However, Twitter would have full control over which tweets get promoted and which don't. And it's unclear how many promoted tweets businesses will get for their $99, and what kind of reach is guaranteed, if any.More news: Sen. McCain returning to Arizona for brain cancer treatment
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With these methods - minus the trends-, you pay per engagement and manually select what to promote, how and when.
Invitations to the new service were extended to previous users of Twitter ads according to an email sent out to targeted users. With growth stalling, the company is seeking new ways to bring in money, and its latest idea is a tweet promotion service for a fixed monthly fee.
The new program also comes after Twitter announced another dismal quarter of earnings, in which the company had no user growth and saw ad prices decline.
Twitter now has 328 million monthly active users (MAUs) - the same number it reported in the first quarter of 2017.
Twitter's net loss widened to $116.5 million, or 16 cents per share, in the second quarter ended June 30, from $107.2 million, or 15 cents per share, a year earlier. Targeted users are being given free 30-day trials of the new service.
Last year, it generated $8 billion in global revenues.