DTA provisions (IAS12, Revision, Q9)

I struggle to understand this formulation: The existing debit balance on the current tax account of $2.4m represents the over/under provision of the tax liability for the year ended 30 September 20X2. Tutorial note: To eliminate the “over/under provision” on deferred tax described as a debit must be current year expense (i.e. prior year was underprovided).
To understand this question I need to know when is an existing debit balance on the current tax account an over provision and when it is an under provision? And why is it an underprovision in this particular case?
I tried ACCA AI and the answer was over provision, so unlike the ACCA solution, a subtraction, not an addition took place.
Thank you.

Speculate Co is preparing its financial statements for the year ended 30 September 20X3.

The existing debit balance on the current tax account of $2.4m represents the over/under provision of the tax liability for the year ended 30 September 20X2. A provision of $28m is required for income tax for the year ended 30 September 20X3. The existing credit balance on the deferred tax account is $2.5m and the provision required at 30 September 20X3 is $4.4m.

Calculate the total amount which will be recognised as an income tax expense in the statement of profit or loss for the year ended 30 September 20X3.

$

The correct answer is $32,300,000.

WORKING
$000
Deferred tax provision required at 30 September 20X3 4,400
Provision at 1 October 20X2 (2,500)
Increase in provision (expense) 1,900
Write off under provision at 30 September 20X2 2,400
Income tax for the year ended 30 September 20X3 28,000
Charge for the year ended 30 September 20X3 32,300
Tutorial note: To eliminate the “over/under provision” on deferred tax described as a debit must be current year expense (i.e. prior year was an underprovision)