This message appears when you add an image which is about half the recommended number of pixels for the size you are trying to order.
Even if you are uploading a “full res” image from you camera, this may not be big enough for many large sizes.
If you shoot in RAW, you may need to check your export settings. Many people export 11×17 or 12×18 images, but these may need to be re-exported at the size you would like to print @ 125-300 dpi or higher if you need to crop.
11×17 @ 300 dpi (dots per inch)
= 11×300 = 3,300 pixels by 17×300 = 4,950 pixels
You would like to order a 24×36 print
= 24×300 = 7,200 pixels by 36×300 = 10,800 pixels
Your “full res” image is less than half the size recommended for a 24×36 enlargement.
We recommend that you re-export your image, then redo any Photoshop adjustments or retouching.