Since AppBuilder 3.4, we started downloading application packages directly from Amazon in the AppBuilder In-Browser and Universal clients. This goes for the Windows client and the Extension for Visual Studio as well, but the change there was introduced earlier. This said, if you are using any of those clients, yo might need to whitelist the Amazon Elastic IPs. How to do this is explained here
If the above doesn't help however, or you are developing in the AppBuilder Command Line Interface, I will require some further information in order to assist you. For example, a Fiddler trace
should be sufficient. Still, have in mind that Fiddler traces may expose sensitive information, thus I don't recommend posting them publicly.
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