To add a frame or hanger to your art prints or posters order you can:
From the app, select the Format and then tap on Frames to see the available options:
From the website: select it when you chose your poster/art print size and design
Select a frame or hanger when you are editing your photo poster from the editor:
Or directly, explore all colors, formats and sizes directly from here: https://www.optimalprint.eu/frames
Note: Sizes and colors are subject to stock availability.