Under the Income Tax Act, all payments made by a resident to a non-resident must be disclosed. The purpose of deducting taxes at source and reporting them afterwards is to ensure that taxes are collected on time. Form 15CA is a declaration by the person remitting the money, stating that the tax has been deducted from any payments made to the non-resident.

Form 15CB, on the other hand, is a certificate given by a Chartered Accountant certifying that the provisions of the Double Taxation Avoidance Agreement and the Income Tax Act were followed in regard to tax deductions while making payments.

No, it is not compulsory to submit Form 15CB. Form 15CB is an event-based form that is to be filled only when the remittance amount exceeds Rs.5 lakh during a financial year and you are required to furnish an accountant certificate defined as per Section 288 of the Income Tax Act, 1961.

Only the Digital Signature Certificate can be used to e-verify the Form 15CB (DSC). The CA's DSC must be entered into the e-Filing site. The deadline for submitting Form 15CB isn't fixed. However, it must be submitted prior to the remittance.