Artwork contains low resolution images (dpi)

Convert the Low Res images to High Res Images

Tutorial for Adobe Illustrator
Tutorial for Adobe Photoshop

Software Illustrator

Step 01 – Open the file

Step 02 – Resterize the images and Background Design to 300dpi (single Background images)

Step 03 – Change 72dpi to 300dpi and Background choice Transparent than click OK

Software Photoshop

Step 01 – Open the image

Step 02 – Check the Image Size

Step 03 – Check the Resolution

Step 04 – Change 72dpi to 300dpi than click OK