Connecting module's link to the ground plane

Hi all,
I’m trying to simulate a tether connected to the drone on one side, and to the ground plane on the other side.
I have created a separated modules for the tether and the x500_tethered, inside the px4-autopilot/Tools/simulation/gz/models/ folder.
I compile the simulation with a custom command: make px4_sitl gz_x500_tethered, which means I’m using the default world and its ground plane.
I have tried different approaches to connect them but none of them seem to work as intended. the closest i got was to set the mass of the last link to 100KG.

What would be the right approach to connect the last link to the default world’s ground plane? Thank you in advance!