Determination of Taxable Proportion: certificate procedure for tax deduction on payments to non-residents under section provisions. The payer may apply electronically in Form 15E for a certificate determining the appropriate proportion of a non-salary sum payable to a non-resident that is chargeable to tax. The Assessing Officer must verify chargeability under the Act and any double taxation arrangement, consider specified information about the recipient's tax liabilities and payments, and may issue a person- and period-specific certificate fixing the proportion chargeable; the certificate is valid only for the named non-resident and period unless cancelled, and fresh applications may be filed around expiry.