There are often a number of reason why balances do not match across various reports. A common reason is timing.
Timing is a common reason for why report balances don't always match across various reports.
This article specifically explores the relationship between the Accrual GST Report (BAS Summary) Accrual Profit & Loss Report.
The first thing to check is to ensure that the As at dates on both reports are the same.
If those are the same, the next thing to look for are credits & write-off's.
When a credit is added into the system, from a Journal/P&L perspective this is not income, it is just an asset that will sit on the balance sheet. Only once the credit is applied to an invoice is it effectively moved to the P&L. If you have a credit received in Dec but the invoice is raised in Jan then it will not be reflected on the P&L for Dec, but it will be for Jan.
In terms of the GST Report, the GST rules are that the GST needs to be recognised at the time the money is received, not when the invoice is raised. Therefore in the above example the invoice is being raised at a later time. Note: GST is recognised when the Invoice is raised (not when it is paid) when the invoice is raised under Accruals GST, but not when the payment is received first.
As such, due to the time difference, the P&L and the GST Statement can end up having significant differences in Income if Credits are used, which is the case in this situation.
In order to reconcile the GST Report and the P&L for the same period, you need to start with the GST Income then add back the Used Credits and subtract the Credits that were received for the period.
Additionally Write-Offs are presented as negative Income in the GST Report, but an expense in the P&L, so you would need to add back the Write-Offs as well to get the figures.
Here is the calculation to use on the GST Report:
Start with All Income Total
Add Credits Used
Less Credits Received
Add Write Offs - 0
Total = 187315.14
Then compare this with the P&L Income for the exact same period - he two figures should now be the same.
If you find that the above is happening because of credits, a suggestion would be have the funds deposited into trust and when the invoice is raised a Trust to Office transfer can be completed resulting in the receipt being created after the invoice. If done this way, there will not be any "credit" issue as such, however for any write off's you would still follow the same calculation as above.