mbsync: 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 CentOS possible default full paths are:

/usr/bin/mbsync - from package: isync

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mbsync - from package: isync

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

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