For technical support with the Flow mobile apps, you should contact the Flow support team directly. To do so, visit flow.microsoft.com/support and click the Contact Support button in the bottom right of the page (see green box). Sorry I can't link directly, when you click on the button it generates a unique URL. 
In the past, they've also provided this email address (flowdev@service.microsoft.com), but I am not sure if it is actively monitored or not. When contacting support, along with full details of your issue (including screenshots), be sure to provide them with the model of your phone, the version of the app you are running, and the version of your phone's OS you are running.
Providing this basic information from the outset should help expedite your support experience.
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