validate-json: 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/validate-json - from package: php-JsonSchema

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

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