Perl: Can't locate object method

I would like get the size of one file who is stored in a ftp server

I am able to connect to the ftp server, but I cannot get the size of one file

For example, I try to use $ftp->getSize(5), and I get the followed message :

Can't locate object method "getSize" via package "chilkat::CkFtp2" 
at C:\Users\mike\Desktop\WinDev\abc\Copy Ftp 2\TestFileSize.pl line 37.