Apple reportedly lost a court appeal over two infringements of patents owned by a subsidiary of PanOptis Patent Management, the latest twist in a legal case which began four years ago.

PanOptis Patent Management and various subsidiaries sued Apple in 2019 over the use of patents without proper licensing, with the iPhone maker ordered to pay $506 million following a trial.

A retrial in 2021 cut the penalty to $300 million, a sum Apple is fighting.

Reuters reported the legal battle between Apple and PanOptis Patent Management resulted in six separate trials and three appellate hearings in London.

The latest battle regards two patents controlled by subsidiary Optis Cellular Technology.

In 2022, the UK High Court ruled the patents are essential to 4G standards and Apple had infringed them through use in products including iPhones and iPads.

The decision was appealed in May, but the UK Court of Appeal has now dismissed the case after agreeing with the High Court’s decision to “reject Apple’s argument for non-infringement” due to the patents being deemed essential.