nfc-relay: 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/nfc-relay - from package: libnfc-examples

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

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