Careful! Do not modify this unless you know what you are doing!
As you probably know, the way ShortPixel Adaptive Images (SPAI) works is it edits the URLs of your images on-the-fly, when your visitor loads the page (How does ShortPixel Adaptive Images work?). It does that because the optimized images are served from our CDN. These URLs look like this: https://cdn.shortpixel.ai/spai/q_lossy+w_794+to_webp+ret_img/https://www.example.com/wp-content/uploads/2018/06/IMG_0169-1.jpg
The API URL is the first part of the URL (https://cdn.shortpixel.ai/spai ), and it basically tells SPAI where to look for the optimized images. If you decide you want to use a different CDN to deliver the optimized images, you’ll have to change this field. For more information about this, check this article.