google xml sitemap generator plugin not working

hi guys,

i’m building a new site, and installed and activated the google xml sitemap generator plugin, but it tells me this:
# There was a problem writing your sitemap file. Make sure the file exists and is writable.
# There was a problem writing your zipped sitemap file. Make sure the file exists and is writable.

i’ve created the 2 files and set write permissions, but it still gives me that message, and sitemap of the site cannot be generated. i also tried realtime sitemap plugin, but still, the page https://www.mysite/sitemap.xml returns a not found page.

what should i do?