Problem with gnuradio connection to ADALM2000

1. I have installed all Linux (Ubuntu 18.04) drivers for libiio correctly.

2. I have been able to connect with the ADALM2000 with info_iio command and receive a listing of ADALM2k services.

3. I have installed Scopy software and been able to run the delightful software.

4. However, as seen in the gnuradio flowgraph below, I dont seen to be connecting to ADALM2k via the IIO Attribute Source block, even when I am using the correct URI, USB:2.3.5 that I used for connecting to ADALM2k via iio_info.

My aim is to capture a square-wave waveform being fed to the ADALM2k from a function generator and to delay the waveform by say 300, 350 and 400 microseconds. The flowgraph below is a simulation that ran successfully.

The flowgraph here is the one I have a problem with:

Thanks in advance...