Custom commands are shell commands. Not WinSCP commands.
If you want to use WinSCP commands, you have to execute WinSCP (another instance) in a custom command to execute your WinSCP commands.

This is covered here:
https://winscp.net/eng/docs/guide_custom_commands_automation

Commands -> Static Custom Command -> Enter...
and then type as local command:
put -resumesupport=on c:\_temp\temp2\*.txt /username/tmp/temp_dir/

How exactly did you try to use this in GUI?

Hi,
I'm not familiar with these funcionalities and I have a problem to create simple custom command which would uplolads files from local dir to remote dir.
When I use my command in script it works. Byt when I try to use it in GUI mode nothings is happening.
Could anyone know what I'm doing wrong?

My simple script:
opne scp:// .....................
put -resumesupport=on c:\_temp\temp2\*.txt /username/tmp/temp_dir/
exit