Thanks for asking question! As you mentioned you are in Free Trial Azure Subscription. If I have understood right you are getting 503 service unavailable error. There might be possibility that your app has exhausted its resources. If this is the case scaling the App Service Plan to a paid one, say B1: Shared might be helpful.
Also you may want to know that App Service provides an intelligent and interactive experience to help you troubleshoot your app with no configuration required. When you do run into issues with your app, the diagnostics tool will point out what’s wrong to guide you to the right information to more easily and quickly troubleshoot and resolve the issue.
You may refer to Troubleshoot HTTP errors of "502 bad gateway" and "503 service unavailable" in Azure App Service
More details : Azure App Service plan overview
Let us know if you have any question on this or issue remains.