Usually the bonus portion of the contract is paid at signing. The teams are allowed to spread it over the length of the contract in order to moderate the cap hit. The only real exceptions to this are roster bonuses and workout bonuses which are paid on a specific date.... Much like the 2.5mil roster bonus AB has coming on March 5th
First here is what I found about bonuses.
Bonuses
There are several different types of bonuses a player can earn.
A signing bonusis what is known as “guaranteed money.” This is cash a player earns just for signing a contract. Signing bonuses are typically spread throughout the life of the contract, but if a player is released, the team must pay him the rest of the bonus he is due.
For instance, if John Doe received a signing bonus of $1M for a four-year deal, each year he is paid $250,000. If John Doe is released after the first year, he is due the remaining $750,000. The amount of money owed is known as dead money.
For clarification, the signing bonus is the total amount the bonus is worth. A prorated bonus refers to the amount of that bonus a player is paid each season (so in the above example, the $250,000 each year is the prorated bonus).
Then there are roster bonuses, which is what a player may earn for being on an active roster at the beginning of the league year. Reporting bonuses are similar; these are bonuses for reporting on time for workouts or training camp. These bonuses are paid out in a year-by-year basis, according to the terms set forth in the contract.
https://www.cincyjungle.com/2018/9/6/17600618/nfl-salary-cap-2018-everything-to-know-about-salaries
According to Spotrac here are his numbers.
2019
Salary - $$12,625,000
Bonus - $3,800,000
Restructured bonus - #3,240,000
Roster Bonus - $5,000,000
2020
Salary - $$11,300,000
Bonus - $3,800,000
Restructured bonus - #3,240,000
2021
Salary - $$12,500,000
Bonus - $3,800,000
Restructured bonus - #3,240,000
SO if I am understanding this correctly based on the article, if the Steelers trade Brown they will have to pay him $21,120,000 and take that hit all in 2019. That would be the total of the three years of bonuses and the restructured bonuses. They would not have to pay him the roster bonus if they trade him before the new NFL year.