@Doug_Armand All tables must have unique keys in order to work properly, so you’ll need to give each row in Sales a unique key, even if it means adding a new column to the Sales sheet/table.
I’m guessing your app is an attempt to track sales of images. The Images table records the individual images, and the Sales tables records sales and the image sold with each sale. If so…
Each image in Images is a distinct record, and should have a unique KEY column value.
Each sale in Sales is also a distinct record, and should also have a unique KEY column value. Each sale record in Sales should also have a Ref-type column that references the row in the Images table that describes the image sold. The value in that Ref column will be the KEY column value in the Images table for the image.