I cannot use Web App Builder when i'm not in the same network of Portal's server. And it's need to fix the Hosts file to map between private server ip with the hostname. There is Netscaler to do ssl offload in this site. I don't know how to fix this. Please help me, thank you.
Web AppBuilder does support accessing content from Portal for ArcGIS on a different domain. However, given the nature of your question (e.g., working across 2 network domains, security settings, using 3rd party components, etc.), it might be best for you to contact Esri Tech Support so they can investigate and help resolve your issues.
Hope this helps,