Air Con Regas Port

I'm trying to regas my C4 Picasso air con. I've located what i believe is the low side service valve but the hose connector won't attach to it properly. It mostly fits on but is not pushing the inner pin in so the coolent just bubbles out of the side of the connector.

I bought this:
https://www.amazon.co.uk/gp/product/B004XZPANK/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

has anyone done this to their c4p?