CAT_VALIDATION_ERROR_TOO_MANY_ADDITIONAL_IMAGES indicates a single product carries more supplementary images than Snap accepts. Trim additional_image_link to Snap's per-product cap (currently up to 10 extras) to clear the error.
Snap Catalog Manager requires product images that are publicly reachable, sized within the platform's bounds, in supported formats (JPEG/PNG typically), and free of overlays, watermarks, retailer logos, or text callouts. This issue trips when one of those constraints is broken.