I can think of two things you want to check in order to be able to pin your website images to Pinterest.
First, Pinterest does have a minimum and maximum image size requirement. If your images are too tiny or too large, pinning won’t work. The minimum seems to be 80 x 80 pixels. With very large images, you may get a time-out before the image can upload.

Second, check the name of your image files to be sure there isn’t anything odd in there. We recently helped a customer who couldn’t pin from her website, and it was because the images were labelled as .JPG with capital letters, instead of the traditional .jpg.

You can take a look at this Pinterest Help Center page, to see if there is anything helpful to your situation: try the Pinterest help page. If not, you can click the “Contact Us” link at the bottom of the page, and write in to see if someone from Pinterest can troubleshoot why you can’t pin from your website.

Alternatively if you are using using both Autoptimize (plugin) and Cloudflare (CDN), please make sure to:After all/any/each site edit(s):
1. Clear the cache plugin.
2. Clear the CDN Cache and force an update with CDN.
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Please review with each how that all works.