This turns out that it was actually working fine, but just that static URLs in text fields weren't working because of a recent Kentico 13 upgrade. The URLs changed from something like /getattachment/Insights/SI-Group/ULTRANOX-626-Antioxidant-Food-Packaging/Text-Area/spacer-SIGROUP-1.png.aspx" to /getattachment/c27f0a2b-07fc-47b6-a13a-decc361cfbac/spacer-SIGROUP-1.png?lang=en-US. When we just updated this, it may have been cached or something, because it wasn't working... so, we assumed we needed "cms.chempoint.com" in the URL to make it work. But turns out, that Kentico just does this for us on the front-end (where both the cms URL and MVC site URL both work to render the image). So, thanks, Juraj for promping us in that direction!
Here's how we were updating - through the WYSIWYG Editor:
And then here's what the code outputs:
<img alt="spacer-SIGROUP-1.png" src="/getattachment/c27f0a2b-07fc-47b6-a13a-decc361cfbac/spacer-SIGROUP-1.png?lang=en-US" title="spacer-SIGROUP-1.png" />
And, when we consume this field with the relative URL on the front-end (website/presentation URL: www.chempoint.com), i thought the URL was incorrect (with www.chempoint.com), but that actually worked fine:
This works: https://cms.chempoint.com/getattachment/c27f0a2b-07fc-47b6-a13a-decc361cfbac/spacer-SIGROUP-1.png?lang=en-US
This also works: https://www.chempoint.com/getattachment/c27f0a2b-07fc-47b6-a13a-decc361cfbac/spacer-SIGROUP-1.png?lang=en-US