What are the requirements to be fulfilled for exercising substituted performance?

Specific Relief Act-Section 20.  Substituted performance of contract- (2) No substituted performance of contract under sub-section (1) shall be undertaken unless the party who suffers such breach has given a notice in writing, of not less than thirty days, to the party in breach calling upon him to perform the contract within such time as specified in the notice, and on his refusal or failure to do so, he may get the same performed by a third party or by his own agency: Provided that the party who suffers such breach shall not be entitled to recover the expenses and costs under sub-section (1) unless he has got the contract performed through a third party or by his own agency.