URL of subfolder site gives error when i change permalink from default to post

Sorry for the late reply, I realize the situation may have changed, but it doesn’t look like there is a site at /hindi/ at all. In any case, if there was, it should behave as a completely independent site, not redirecting elsewhere. For this to happen, the .htaccess rules in both public root and /hindi/ must be appropriate. Also, the site and home URL settings must be correct for each site.

If the site is using DB data copied from elsewhere, there are numerous places where the URL needs to be corrected. Usually the export/import tools will adjust these, but if you copied the raw SQL data, all URLs need correction.

@bcworkz Plz check again here is the site url https://learnforget.com/hindi/ there is a sample post also there, plz click on that you will find the issue. Let me clear one thing i am not a wp developer, so plz give me a solution in easy way so that i can understant it clearly.

Be sure you’ve correctly configured your site according to Network Admin > Settings > Network Setup. Be sure there are no other WP related rules in .htaccess other than those shown here. Some people neglect to remove the old single site rules, which cause trouble.

In Network Admin > Sites, follow the Edit link for /hindi site. Open the Settings tab and ensure both the home and site URLs are correct.

If you still have trouble, network deactivate all plugins and all themes except twentytwenty. The Hello World link on the /hindi subsite should now work. Restore your main site’s normal theme and network activate the plugins, then activate the ones you normally use for your main site, one at a time, checking the /hindi/hello-world/ link after each. Main site themes and plugins can influence subsite behavior if not coded correctly for multisite. When you again have trouble with the /hindi subsite, the last activated module is the cause.

@bcworkz Hello, https://learnforget.com/hindi/index.php/2020/11/09/hello-world/ check this url its working, but main issue is its working only till i use the default url stracture, it starts giving issue when i change the permalink structure to post name or any other.

Having index.php within the permalink to posts is unusual. Yet your hindi subsite’s home page works as expected. Strange.

The inability to update permalinks can be caused by WP not being able to write to .htaccess. Via FTP or your hosting file manager, try setting its file permissions to 664. This introduces a bit of a security risk. Note what it currently is (often 644) and restore that value if 664 has no effect.