Investment proofs -Section 80DDB

I added a claim under Section -80DDB with all the documents like Prescription, Bill and Test Reports. Still it got rejected and it will be only approved when Form -10I is added as proof. Is this form really required? Ques.I have seen on many platforms that this form is not required. On official site -it said taxpayer should obtain a copy of 10-I issued by relevant specialist working in a Govt. Hospital. Ques.Patient was treated in private hospital.why need a certificate from govt. Hospital