The Ripl app doesn't request screen overlays but other apps on your phone may use screen overlays to show their content on top of Ripl (or any other app you are using). An Android 6.0-only bug prevents the operating system from granting permissions when screen overlays are on. If some of your other apps use screen overlays you may run into a screen overlay detected message when the Ripl app requests permission (to access your photos or save the animation to your device or uploading your own logo).
A workaround for this is to temporarily turn off the overlay setting for apps that are interfering with the system permissions dialogs. To do this open your settings and turn off the screen overlay settings for all other apps. Then return to the Ripl app and "allow" the permissions to be granted. Once you've accepted the permissions in the Ripl app, return to your settings and turn screen overlay back on for the other apps.
Typically Ripl will only need to ask for each permission once, so you shouldn't have to continually turn your screen overlay settings on and off.