主codeIgniter项目中的子项目不起作用，找不到错误

I have CodeIgniter project and I put another codeIgniter project named "admin"inside that project

structure looks like this

    codeIgniter project
       admin (this is another codeIgniter project)
       application
       public
       system
       user_guide
       vendor
       few php and htaccess files here

I access normal project like example.com and to access admin project I work like example.com/admin these all are working fine, but now I added another codeIgniter project inside main project "api" it does not work.

Now structure looks like this

    codeIgniter project
       admin (this is codeIgniter project)
       api (this project does not work, url issue)
       application
       public
       system
       user_guide
       vendor
       few php and htaccess files here