what node set are you using on structure? I would start with just the vid node by itself
do you have sync run? This one may not be necessary I’m forgetting offhand if the RGB inputs can also pull sync like the composite input. If it does need sync you could use the vidiot sync loopthrough output or just the regular composite output into the sync input on the back of structure. I’ve always got my structure syncd up to the entire system so I’m just not 100% sure if that is necessary.
you could also just take the composite output from the vidiot into the composite input on the structure to make sure things are working.
when you have tried this are you getting a video signal out of the composite output on the vidiot before trying to input it into structure?
do you get a video signal form the structure composite output with other node sets?
do the cables you are using (composite and the 1/8 euro) work in other situations?
if none of that helps get a picture of the front of the structure and the connections between the two.