FarApp hosts your images using Amazon’s S3 service, which is highly reliable and scalable. So if you see this error, it’s most likely not due to a failure to connect. As described at the following link, the color model of your image must be RGB and not CMYK (see CMYK Color Format section):
If you review the information at that link, there are also instructions on detecting whether your image is in the CMYK color format and how to convert it to RGB if it is. Once you update the image, it should re-upload to eBay successfully.
eBay also has the following page which you can review for more information on this error: