Sorry for not replying before.
I'm afraid due to a very unfortunate bug we had a long time ago, some of the transfer history data was lost. I cannot fix that by hand, it would just take too long and some of the data is lost irreparably. However, we do have the economy transaction data that shows us you received $4.8M after taxes, but we don't have the tax amount. While I believe you to have sold him for $5M, I cannot code that in with the missing variable (taxes). If I used the smallest tax amount as minimum (3%, I believe), your transaction would not give us a high enough amount for the achievement. So, the problem needs to be fixed via a code change to ensure fair play (everyone's data should be fixed, not just yours) but it's not an easy one to tackle. If I made the change to give users the achievement based on the economy transaction + 3%, it would probably fix the same issue for some other managers, but not for you, since $4.8M + 3% is still less than $5M.
There's another possible approach; we could change the achievement text to say something like "Received a lot of cash for a player (after taxes)" and use the correct and complete data from the economy transactions to recalculate the receivers of the achievement. It would then make sure we have the right amounts. This would also mean that a lot of people would lose the achievement due to the tax difference. I'd love to hear some opinions on this.