The fee is officially undisclosed, I imagine each side leaks their preferred version for example the buying club will give the basic fee to make it seem like they got a bargain, the selling club will include sell ons, potential totals etc. to make it seem like a better deal for them.
It's not 1.8m. At a massive stretch it could be 1.8 with lots of add-ons that are very unlikely to happen. eg. 1M basic fee, 200k if he makes 20 appeareces, 200k if he gets 12 assists, 300k if they get promoted and a 10% profit sell-on clause for example would be around 1.8M transfer, but we only get 1M right away.