someone will ask you how you select the gradient.
You may copy from a swatch just using the Bucket, otherwise you should use the Eyedropper on the object to copy from and the Bucket to copy. You may swich between the two by holding Alt/Option.
It does not appear that you have posted to the Adobe Illustrator Forum, (just click), as others have suggested.
You will get an answer there, and probably very quickly.
Also, in your next post, the screen-cap, or illustration did not attach. Before you post in the Adobe Illustrator Forum, this ARTICLE might be helpful.
30 hours and I have not gotten an answer to what seems a simple question:
why can't I fill with a solid colour the closed path that I created with
the pen tool?
You did receive an answer before posting this. And you must remember that this is a user to user forum with no Adobe personnel asigned to it, so that you have no reason to expect instant answers.