Sometime when submitting an ad an error will appear notifying you that images are required but you have already added them.
This most commonly occurs when you exceed the image size limit. There are two restrictions for images:
A single image cannot be larger than 15mb
All combined images cannot be larger than 20mb total
We recommend images to be converted to .jpg format and kept under 1mb each.
There is a endless list of software and tools that you can use to compress your images but you may already have one on your device already, such as:
Photos App (Windows 10)