how do i write off wht receivable in manager system?
If you are asking about Withholding Tax, then this is explained here Account for withholding tax on sales invoices | Manager
Scenario 1: Amount in WHT in balance sheet - $5,000.
Tax assessment -Tax payable $6,000
Create Purchase invoice to Tax Authority (Supplier)
Scenario 2: Amount in WHT in balance sheet - $8,000.
Tax assessment -Tax payable $5,000
Create Sales invoice to Tax Authority (Customer)
@arts, can you please be more specific about what you are trying to do? What do you mean when you refer to writing off withholding tax? Taxes are not normally written off. When you owe them, they are paid. If you have overpaid, money is received from the tax authority.
Also, are you referring to tax withheld at the source, as in the Guide @Joe91 linked? Or are you referring to a tax deducted from someone’s payslip?
@AJD, it is not clear what you are suggesting or why. Nor is it clear why you are using sales and purchase invoice to do it. Can you please clarify?
In Manager, if you mark an invoice as having WHT, it books the WHT amount onto the balance sheet as a receivable. I.e. often WHT will be “reclaimable” from the authority that demands it, via Dual Tax Agreements (in the case of international WHT) or a local fiscal authority for local WHT. If you cannot recover the WHT from the authority that claims it (i.e. there is no DTA with the country that demands the WHT), then it really isn’t WHT (as far as Manager understands it), it is another cost that you have to pay.
In this case, you should create a new cost account on the profit and loss for WHT paid (to wherever), and then after creating the invoice (don’t mark it as having WHT), make a Journal Entry (same date as the invoice), booking the amount of the WHT on the invoice to the cost account you just created (CR customer, DR WHT cost account).
The invoice will now show as owing the amount less the WHT, and you have a cost amount on the P&L for the WHT your customer deducted from your invoice.
tax withheld at source. Thanks
You haven’t answered the questions you were asked last May !
That would be a good starting point 
Let’s start with what you mean by writing off withholding tax. Generally speaking, you do not write it off. You can inform customers they should withhold it. You can withhold it when paying suppliers. You can remit amounts withheld to the tax authority. You can use amounts remitted by your customers on your behalf when settling taxes due. All those are explained in the Guides I linked to when I responded to your other question today.
And please, do not scatter your discussion of a topic through multiple threads.