Runtime Frequency Adjustment via ZMQ - Format Error

Dear Community,

I want to change the freq from another applicatio during runtime using zmq, I have tried this by setting the default freq variable to 10, but the message coming from zmq is not converting to appropriate format. Could you please help me to rectify this issue?
terminal output:
sub_msg_source :error: Invalid PMT message: pmt::deserialize: malformed input stream, tag value = : 51
sub_msg_source :error: Invalid PMT message: pmt::deserialize: malformed input stream, tag value = : 51
sub_msg_source :error: Invalid PMT message: pmt::deserialize: malformed input stream, tag value = : 50
....  

Regards
Muhammad Anas