Every Open Graph image OpenGraph+ generates for you uses one rendering credit. That covers the first time a page’s image is built and each time you refresh it after a change.
Shares are free. Once an image is rendered it’s cached and served from the edge, so a link that takes off costs you nothing extra no matter how many times it’s opened.
Your plan includes a monthly allowance, and most sites use far fewer credits than pages because unchanged pages never re-render.