@kalibur It looks like the developers of that app did not code the app so that it would even request storage permission. The developers of the app have to configure the app to request that.
My suggestion is to ask in the chat for a copy to be sent to you. Ensure that you get the copy before closing the chat or app.
Failing that, another option would be to capture screenshots.
I have had this with some apps where "storage" was not an allowed permission. I went through and allowed individual items until the message finally cleared. Try going to settings>apps>scroll to the Myatt app> and then click permissions. I want to say mine "worked" when I allowed photos and videos access....because behind the scenes that enable the storage. But I can't recall for sure. One of the permissions "fixed" it even though "Storage" wasn't an option on that specific app.
