Personal travel assistant developer Mezi had raised $9m in an American Express Ventures-backed series A round 18 months ago.

Payment services firm American Express acquired Mezi, a US-based digital travel assistant developer that is also one of its portfolio companies, for an undisclosed amount on Tuesday.

Founded in 2015, Mezi has built a personal assistant that combines artificial intelligence technology with human customer service agents to help users book travel, accommodation and dining.

The platform retains a profile on each user that is automatically updated, helping agents to make personalised recommendations. The technology has been powering AskAmex, a personal…