I have the following Patch on Pure Data. In it, I want to send the value of the number object to a pipe in Lua, using the foo object (which I created using pd-lua).
This is the foo object code --> foo.pd_lua
This is the Lua pipe code --> scriptb.lua

Can anyone help me to find out the error?

I'm really not sure here, but maybe you have to close the pipe in the Pdlua object, so your Lua script can open it? I see in your .pd_lua code that you close the pipe only when you destroy the object. Did you try to close it right after your flush it? Because in the Lua script, you close the pipe in every loop iteration.