How do you create the vendor-hosted SharePoint Online app?
To my knowledge, Office 365 only accepts apps with low trust.
If you are creating the Azure and Visual Studio provider-hosted app and you want to add the app to SharePoint Online, you must package the app and then go to SharePoint Admin Center> Apps> App Catalog> SharePoint Library Apps and the app Upload app file to this library.
Once you've trusted the app on the SharePoint Online site, you can add the app directly to your website. The following article provides more information about adding a vendor-hosted app to SharePoint Online. This can be helpful for you:
http://sharepointpals.com/post/Step-by-Step-Procedure-to-Create-a-Low-Trust-Provider-Hosted-App-for-Office-365-and-Host-the-AppWeb-in- Azure WebSite