Show picture from "image" metadata in iOS Twitter composer




I’m working as Solution engineer in my company. We have a mobile application supported on iOS, Android, Windows and Web. Every item shared from the native apps is actually a URL pointing to our web-application.
We implemented a metadata serving service and a template generation service to generate nice sharing outputs on Twitter. When Twitter bot parses our sharing url, we redirect it to those two services. This logic is based on Twitter bot’s user agent.

Our issue is when it comes to the preview of our sharing URLs in Twitter composer on our iOS application. The picture displayed there is not the image we set in the metadata but a screenshot of our web-application. Since our web-application needs to load quite many resources at launch, this screenshot alway represents our loading page and as a result, the experience is broken.
In addition, since the service that takes this screenshot does not have a specific user agent, we cannot redirect it to our meta-data service service.

Would you have suggestions to fix the preview generated in Twitter Composer? Is-there no way to have Twitter use the image metadata for this preview?

Thank you!