I've written the below code which looks fine as per the instructions given in the challenge.
But I'm facing an error when trying to resolve the challenge. Please help.

Error: Executing the 'generateRandomContacts' method failed. Either the method does not exist, is not static, or did not return the correct set of Contact records.

Code:

public class RandomContactFactory {
    
    public static List<Contact> generateRandomContacts(Integer n, String Lastname)
    {
        List<Contact> ct = new List<Contact>();
         Contact c = new Contact();
        for(Integer i=0; i<n; i++)
        {
           c.FirstName = 'Test '+i;
           c.LastName = Lastname;
           ct.add(c);
        }
        
        return ct;
    }

}