Using a channel without a defined signal error

I am curious whether anyone knows how to resolve this issue, as I am currently unable to overcome this hurdle. I have even simplified my code for testing purposes, yet it continues to produce the same error.

Any suggestions?

Code

PROC main()

TestSignReset;
TestSignDefine 1, 9, ROB_1, 3, 0.001;
WaitTime 0.2;
ntest_val := TestSignRead(1);
TPWrite "Torque Value is: " \Num:= ntest_val;

ENDPROC

From the Instructions, functions and datatypes manual:

Only test signals for external axes can be reached. Test signals are also available
on request for the robot axes and for not predefined test signals for external axes.