Input tax credit entitlement requires invoice, receipt, actual tax payment and return filing; nonpayment prompts credit reversal. Registered persons may claim Input Tax Credit only if they possess a tax invoice or prescribed document from a registered supplier, have received the goods or services (including deemed receipt), the tax on the supply has actually been paid to the Government (in cash or by permitted credit), and the claimant has filed the return under section 39. Credits for goods received in instalments attach only on the final instalment; failure to pay the supplier within a specified period requires reversal of claimed credit with interest, while payment restores entitlement. Credit is disallowed where depreciation was claimed on the tax component of capital goods and is time barred by the statutory return deadlines.