If you change your payment method, make sure that your account information matches the credit card information on file with your financial institution.
It can be tempting to install a beta version of iOS to have a first peek at upcoming features, especially when brand new software is being released, such as iOS 11 which offers a number of significant new few features.
The iOS signing window is one of the more obscure details related to the iOS & jailbreak community. The signing window is the window of time in which a certain iOS firmware is able to be updated or downgraded via iTunes.