iOS 9.3.5 to iOS 12 update on iPad Mini 2
I have an iPad mini 2 wifi + cellular with iOS 9.3.5. On the Settings, it says that iOS 12 is available on my device. However, there is no option to download and install it using the iPad (Grayed out) and it only says there to update it using iTunes which I did! After downloading the 2.72 GB update, it will give me an error code 3259. I have contacted Apple Support 10 times, which a senior apple adviser supporting my case but still it won't update. I just need it updated because some apps aren't available which I really need. :( can someone help me here?
iPad mini, iOS 9