The article shows that a mask to use is like *.txt, not .csv.

See also https://winscp.net/eng/docs/file_mask

I used the exact script from:

Contents » .NET Assembly » Examples » Listing files matching wildcard

When I execute the script it returns:
PS C:\sftp script> C:\sftp script\mhd_test_v3.ps1
No files matching ".csv" found

However, there are hundreds of .csv files on the remote server. I have read/write/modify permissions on the remote server. I can list the files from command line but the "Listing files matching wildcard" script is not returning any results.
Am I missing something?