AT+QISEND command when is module serve like as server

HI, i need help for described case.

I use module M95FA to serve as a server (Single UDP connection).
Module works in non-transparent mode.
Also, module is configured to use QIRD command for reading received data.

In configuration process i used following commands:
AT+QIFGCNT=0 // Select a Context as Foreground Context
AT+QICSGP=1,“APN”,“USERNAME”,“PASSWORD”
AT+QIMAX=0 //DO NOT enable multiple TCPIP session at the same time
AT+QIMODE = 0// Non transparent mode
AT+QIDNSIP = 0// The address of the remote server is a dotted decimal IP address
AT+QILPORT = “UDP”,PORT
AT+QINDI = 1// Output a notification statement “+QIRDI: ,,” through UART.
AT+QISERVER=1 //

After command AT+QISERVER, module return SERVER OK.

Another module sends data as a client and i get next message:
+QIND:…

i successfully read message using QIRD:
AT+QIRD=,,,

and after processing message i try to send data with following commands:
AT+QISRVC=2 // select server
AT+QISEND=len

BUT MODULE RETURN ERROR.
Description of command says “If connection is not established or disconnected: ERROR”

How i can establish connection or why connection is not established?