I'm trying to use the mentioned tool with the custom area tool but as soon as I hit the custom sampling, I get the following error: "Could not fill because there are not enough remaining pixels to fill the hole. The change cannot be applied."
There is only one layer which is the picture, this has happened only on macOS. I was using the tool all day in windows, and everything is working fine. But in macOS this behavior is taking place on every picture.
It looks like you don't have any pixels selected to fill with... That bright green on the right is the color that will show the pixels that are selected to be used to fill you space. There are is no bright green overlay on your image. You need have the sky overlayed with bright green to tell PS to use those pixels to fill.
For a small spot like that I would personally use the spot healing brush or the patch tool. content aware fill is overkill.
Melissa Piccone | Adobe Certified Instructor | Adobe User Group Manager