In order to share the file, I used the "..." (three dots) and I clicked on "sharing" (on the website).Then I put the email address of the person, making sure he can modify things, and I sent it. I didn't send a link
I don't seem to see the changes on the website either.
Maybe there is an issue on the computer of the person I shared the file to? When he goes on the website, under "shared files", he doesn't see the "adding" button.