By default, the image ratio of the Collection or Issue Cover in the Universal App is set to 3:4 image ratio. If you're using another image ratio for your cover, you can change the default settings.
Go to Branding > Appearance tab and select the Default Cover Size.
It will open a dialog where you can change your cover image ratio to another standard paper size, which is A4 or US Letter paper size.
If you're using another standard image dimension that doesn't fit any of the available image ratios, please contact support@magloft.com, so that we can assess whether we can accommodate the different sizes or not.
Have more questions? Feel free to reach out to our live chat at the bottom right corner of your Universal App dashboard or send an email to support@magloft.com
Visit the help playlist to get started with your Universal App here.