How to redirect in php project using .htaccess file (redirect url without slash to url with slash using 301 redirect)

Try this:

Redirect 301 /old/page /new/page

or

Redirect 302 /old/page /new/page

Keep in mind:

A 301 redirect is a status code that tells search engines and users the page has permanently moved.

A 302 redirect is a temporary change that redirects both users and search engines to the desired new location for a limited amount of time, until the redirect is removed.