Another wordpress in a sub directory and premalinks

Hello i have web site running at example.com and now i wanna add a whole new wordpress site at example.com/sub i installed wordpress to sub directory and everything was working fine. But after i changed permalinks to /%postname?/, my articles on subdirectory site now giving 404, i tried to edit htaccess but couldnt find a way to fix it.

my main site at example.com is working perfectly fine. but permalinks giving 404 at example.com/sub

can anyone help me about it?

Thank you.