There are two functions used for REXX dll support LoadFuncs and DropFuncs . There is no extensive parameter checking. In the scheme of things, you are responsible to use the commands correctly. This dll is not an exercise to find how many ways you didn't. Besides if you're familiar with client FTP commands you won't have any trouble.
Every command returns results via an 'RC' variable.
No parameter is every changed. Most likely you misspelled a parameter like a domain hostname or didn't pass the minimum number of arguments. PORT is optional. Default is port 21. Use for alternate port.