There's a big problem with the iPad Pro that could ruin its main selling point

Developers are becoming unhappy with a lack of features in the iOS App Store, and they feel it's preventing them from making iPad Pro apps, The Verge reports.

Some of the missing features include a free trial option for apps as well better upgrade support. 

This unease, which has been brewing since Apple announced the 12.9-inch Pro, means that many high-end developers who make Mac apps are not interested in the Pro, killing off one of the main selling points. If there are no professional apps, the Pro is far less appealing. 

The Verge spoke to Pieter Omvlee and Emanuel Sa who make Sketch, a drawing app aimed at designers. The Mac version of Sketch costs $99 (£79.99) but the duo have no plans to launch an iPad Pro app because of the lack of free trial. 

Developer Jared Sinclair highlighted the lack of use cases for the iPad Pro on Twitter. 

Sinclare went onto say that he "wants to see Apple open the path for developers to make sustainable apps for all the niches we never hear about." The company is not currently doing this, he said. 

The iPad Pro's launch has been mired by the long shipping times for key accessories, such as the Pencil and Smart Keyboard, and a charging problem that renders the Pro useless. Apple has acknowledged the charging issue.