Can I claim services render but customer didn't paid

[KatherineC]

In order to claim a deduction for income not received, you would have to report the income as well.

To answer this question, let me define the two main basis of accounting.

Cash basis – You report income when you receive the money, and expenses when you pay them.

Accrual Basis – You report income when the amount is billed and the expenses when you receive the bills (not when you are paid/or pay the bills.)

Unless you report your income on the accrual basis (you bill clients and pay tax on the amounts that have been billed, not just the ones that have paid) then not reporting the income is reporting the loss.  There is no income on the books to write off.

If you are on the accrual system and have an accounts receivable amount representing what you should have been paid, then you can write off the amount billed as a bad debt.