Proofs of eligible investments made by you must be submitted to your employer before the end of an FY, say by 31 March 2021 for FY 20-21’s ITR. It is submitted to ensure that the employer considers these tax-saving investments while determining your taxable income and the tax deduction thereon. Suppose you could not submit these proofs to your employer. You can still claim deductions of such investments at the time of filing your ITR as long as these investments were made before the end of the relevant FY.