How do the one-time plans work?
After the free sign up, you can purchase a one-time plan for processing you images. You can use it for bulk optimizing your Media Library using ShortPixel Image Optimizer, or for optimizing new images uploaded to your website, regardless of your choice: ShortPixel Image Optimizer or ShortPixel Adaptive Images. These plans are recommended for websites that have a large Media Library that needs to be optimized with ShortPixel Image Optimizer.
Please note that one-time credits never expire so you can use them until all of them are exhausted.