Medicare COB Question for IP Stay

Best answers
When a member becomes eligible for Medicare Part A in the middle of their Inpatient stay, how is the biller to submit a claim?
The patient had Medicaid State SSI as coverage upon admission which fell to secondary payor once the patient was entitled to Medicare Part A.

Is SSI responsible for the entire stay?
Do we coordinate with Medicare for the days they are effective?

Thank you for your help!