FTP AT command return an error +CME ERROR: 421

Hi,
I am working with QBG96 modem so I want to upload aws iot certificates to modem using UART from linux environment
connections:
Dout—Rx(linux device)
Din—Tx(linux device)
Gnd==gnd
and I follow the link to upload a file https://nimbelink.com/Documentation/Skywire/4G_LTE_Cat_M1_Quectel/1001933_NL-SW-LTE-QBG96_AWSIoTAppNote.pdf
but it raises an error like : AT+QFUPL=“pvt.key”,1679,30
CONNECT
+QFUPL: 0,0

+CME ERROR: 421
and I eneble the Hardware flow control uisng
AT+IFC?
+IFC: 2,2

so please anyone help me to solve this issue and please suggest me how to upload the files to QBG96 modem.

Best regards,
mmm

HI,
This I did solved.

What was the resolution @Macharla_Mounika ?