Yahoooo…just slightly more than an hour after the official release of the latest version of Shellter, @fancy__04 was kind enough to test it and report an issue.
There is an error while parsing the user defined encoding sequence in Manual Mode which makes Shellter to refuse to use it.
It will be fixed as soon as possible, and I will hopefully release the fix today as well.

Cheers,
kyREcon

I just realised that a recent update introduced a silly bug that would allow Shellter to accept an empty ‘CMD’ command string to execute when choosing the embedded WinExec payload.

Other than that, the payload works fine with the command that you submit, so you won’t have any issues with it.

Will be pushing out the fix in  the upcoming Shellter V [5.3].

Cheers,
kyREcon