At line 9, you're initializing $currentAmount as an empty array:
$currentAmount = @()
Then later you're accumulating [int] items into that array:
$currentAmount += [int]$row.'current'
So that what you have is an array of [int].
Eventually you try to do a subtraction operation with that array:
$remainAmount = $currentAmount - $checkAmount
and it fails.
the [Type[]] syntax in the error message indicates it is an array, and you can't do a subtraction operation on that.