If you want to replace the default background of the Messenger card in your Abandoned Cart or Instant Messenger campaigns, the ideal resolution is 1000 x 520px. If you wish to use a different resolution, please make sure, you keep the image ratio at 1 : 1.91.
The 1000 x 520px width is recommended because of the large, high-resolution devices like iPhone 6S Plus and iPhone 7 Plus. If you only have a 500px wide picture for background, that's fine, even iPhone 7 Plus users will hardly notice the difference.
Don't use light background in Abandoned Cart Campaign
In order to keep the text readable, Facebook puts a 40% transparent black overlay on your image. Nevertheless, we recommend that you avoid white or light backgrounds, as the text might still be difficult to read on them.
Don't do this:
Choose a darker background instead:
I hope this helps. If you have any questions, please contact us on the support chat.