1-make sure your project fully blueprint, no c++.
2-disable all third party plugins
3-leave all default enabled plugins to default
4-if you use Crypto disable it
uncheck any encrypt marks in Project Settings → Crypto( clear encryption and signings keys), uncheck Enable Pak Signing.
5-make sure your cert and provision (valid)
6-uncheck Enable Remote Shader Compile in Project setting → IOS
7-all icons in Project setting → IOS should be the default icons,
you can hack the engine by go to …\Engine\Build\IOS\Resource\Graphics\ first make a backup of this folder then rename all your icons to the same names in …\Engine\Build\IOS\Resource\Graphics\ and replace the default engine icons with your icons(they should be the same name and the same size) then go back to engine and go to Project setting → IOS → icons and click the little yellow arrow for all icons.
if you follow this infos you will be able to package for IOS from computer in shipping and distribution mode to app store.