I want to pay salary in lieu of my notice period. What if my manager doesn't approve my request?

I want to pay salary in lieu of my unserved notice period and want to serve only 15 days. My manager is dodging this saying there is no option for buy-out and I have to serve the full notice. The contact clearly states "The LLP or employee may, at any time during the course of the employment by stating their intention to do so in writing, terminate the employment by giving notice as given below or a salary payment in lieu of that notice. The LLP may require an employee to complete all operative parts of the assignment or project he may be involved in on the date of resignation as determined by the LLP before agreeing to his release. If, in exceptional cases, the LLP agrees to an employee’s requests for an early release, the LLP will recover the salary or part thereof equivalent to the balance notice period. For further details please refer to the Human Capital Policy. The notice period for termination of employment by either side for the various levels shall be as specified in Human Capital Policy of the LLP. " How should I proceed?