Nespresso Inissia Leak from pushfit connector from pump

My krups nespresso inissia is leaking from the bottom. I heard the push fit connecing the pump to the tubing pop out. I found a tiny O ring when I disassembled the machine. I cannot see where this goes as there is already an O ring on the male pump connector. I pushed it back in (leaving the O ring out) and all was well for about 4 coffees and then the connector popped out again and water pumped out the bottom again. Could someone advise on this? Thanks. Please see photos