So I currently have an iPad 3 and I download Instagram regularly using the iPhone only option option in the AppStore. I've downloaded it many times before but this time I keep getting the same message over and over (Other apps I have been able to install as usual it's just this one) I've tried a VPN,I've tried a reboot, I've tried changing the date/time If there are any solutions to this please do help.
That particular site could be temporarily out of service. I'd wait about 15 or 20 minutes and try again. If that doesn't work I'd check using your iPhone if you have one. If you've downloaded Instagram once it should remember you and if you try a 2nd time the Get button on the link will become an Open button. See the image below from my iPad.