I'm using an Iphone 8 with the latest software update. For some reason, I can connect to some servers, but not others. For instance, I can connect to Amazon and all its various sites, such as kindle, Audible, and Prime Video, and also the Mail app; but with others, like Target and Walmart, I can't get through. With others, I get a message saying "unable to connect to server." Have I done something wrong in the setup process? Can I correct this on my own or do I need to go to the phone store? Thanks for any help.