ssvnc: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/ssvnc - from package: ssvnc

You may install the required package with command apt-get install {package}

Error in other languages:
ssvnc: bevel nie gevind nie
ssvnc: comandă negăsită
ssvnc: comando não encontrado
ssvnc: commande introuvable
ssvnc: command not found
ssvnc: käsku ei ole
ssvnc: không tìm thấy lệnh
ssvnc: komanda nerasta
ssvnc: Kommando nicht gefunden.
ssvnc: kommandot finns inte
ssvnc: komut yok
ssvnc: nie znaleziono polecenia
ssvnc: níor aimsíodh an t-ordú
ssvnc: no se encontró la orden
ssvnc: no s'ha trobat l'ordre
ssvnc: opdracht niet gevonden
ssvnc: parancs nem található
ssvnc: perintah tidak ditemukan
ssvnc: príkaz nenájdený
ssvnc: příkaz nenalezen
ssvnc: команда не найдена
ssvnc: командата не е открита
ssvnc: 命令找不到
ssvnc: コマンドが見つかりません