Screws to attach a Ring Battery Doorbell Plus to the Angle Accessory

Hello. I recently bought this unit but the screws provided in the box are too short to attach it to the included Angle Accessory. I've searched online and ordered screws from different sellers on Amazon, but they are all too short. Does anyone know what size these are and where I can buy them in the UK? Also missing is the security screw which holds the battery in place. Where can I buy this please? These are all out of stock on Ring's official website. This is so frustrating, so I would appreciate some help! Many thanks