Can't spawn reverse shell of pentest monkey

Hi everyone, doing a machine which there is a file upload and i am trying to get the reverse shell with the one of pentest monkey.I set the IP address to the one i am getting from hack the box( for the example), and set the listening port to 1234 .then i am using:
nc -lnvp 1234
when I succeed to upload it as a .phar file
(because php is not accepted) and i run iti receive for a second in netcat the a connection but after a second it is closing. in the web server i get this error:

"WARNING: Failed to daemonise. This is quite common and not fatal. ERROR: Can’t spawn shell "

just in order to clarify, i checked,no firewall is on, tried to listen on other ports, and the same problem.