Error Code 21916923
Pictures cannot be edited because this listing has pending offers, or the maximum number of pictures has been reached.
This is caused by a pending offer on a fixed price listing with the Best Offer option enabled, or by attempting to add more pictures when the maximum available has been reached.
If the listing is a fixed-price item, you have a pending offer from a customer which needs to be addressed before you can make changes to the listing. Log into your eBay account and respond to the offer, then try revising the listing on StoreAutomator again.
If you have maximized the number of available photos for the listing, you can revise your pictures in order to use StoreAutomator’s Image Override feature by referring to the article below.
Note: eBay allows you to add up to 24 pictures (maximum 7MB each).