IAS 8 Prior period error correction – an example from ACCA’s Study Hub

Hi Mr,

There is a quiz example from ACCA’s study hub that I am not entirely sure the provided explanation in the solution. Can you help me understand the treatment?

Here is the entire quiz question:
In the year ended 30 April 20X4, the management of Libre discovered that revenue had been overstated by $0.8m in each of the prior three years: 20X1, 20X2 and 20X3.
How should this be accounted for in accordance with IAS 8 Accounting Policies, Changes in Accounting Estimates and Errors?

The solution is:
Restate the opening balance on retained earnings to 30 April 20X3 and reduce the comparative amount for revenue in the financial statements to 30 April 20X4 by $0.8m

The explanation is:
The prior period error must be corrected in the financial statements for the year to 30 April 20X4 (i.e. the first financial statements that will be authorised for issue after discovery of the error) by restating comparative amounts (i.e. reduce revenue by $0.8) and restating the opening balance (retained earnings) for the earliest period presented.

My confusions are:
Why the adjustment is $0.8m?
Shouldn’t the total adjustment be $2.4m, since the question states that each year the revenue was overstated by $0.8m for the prior three years.
And why adjusting the current year ending on 30 April 20X1 by reducing revebue $0.8m? Aren’t the overstatement occurred in the previous three periods?
Or am I misunderstanding the solution.

Thank you.