iPad usb-c accessories not working

Hi, I am trying to connect a usb-c hub to my iPad, to be able to connect a hard- drive. The error “unlock ipad to use accessories keeps popping up despite the ipad being unlocked (& i changed the settings from ‘touch id & password’ to allows usb accessories when unlocked’). I use the hub with my macbook so i do not think it is the issue, i have tried connecting other usb accessories through the hub but to no avail :( Anyone know anything which can help, or do I have to take it in? Thanks