I have never believed in the grand conspiracy theory about the football authorities (ie that the whole structure is corrupt and they all hate City, though some people obviously do hate City) but it is a fact that certain matches have been influenced because it has been confirmed by some former referees.
I don't think it is about "brown envelopes full of cash" (at least outside betting scams) but it is obvious that some referees are cowards. They don't make decisions which undermine the biggest clubs especially LFC and MUFC who have big influence in the decison-making process which can make or break people's career as referees and in senior positions at the PL itself (even vetting the CEO's job)
It is a form of instututional corruption and the fact that someone like Mike Riley has ended up in charge of PGMOL tells you everything you need to know. I don't believe that Pawson was being corrupt with his Jota penalty decision (and it was his decision not the match referee's) but he is weak and has allowed himself to be influenced by peer-group pressure. He is ambitious and doesn't want to rock the boat with powerful people. It is a more nuanced form of a corrupt process.