I need some guidance. I'm installing JetTronics brake and retract valves in my TamJets F-16. I have air tubing from Tamjets, Robart, and Spring Air. Try as I may I can't seem to get any of the tubing to lock into the Festo Type fittings. What am I doing wrong?

This is my first time installing these.

TIA for your help.

Bob