There are two things you need to do then:

1. Assign unique permissions to this list

   
   

   1. The approvers need “Design” level

      
      

   2. The requestors need “Contribute” level

      
      

2. List versioning settings must be configured as below
   
   

   
   

This will generate an extra “Approval Status” column in your SharePoint List.  This field must ALWAYS stay in status Pending!!!