By "last year" are you talking about 2024? Do you have a CRP from your actual 2024 landlord?
My sister in law purchased the house that I have been in for the past 3 years and I pay her to help pay the mortgage, but the house is in her name.
Sounds like you pay rent to your sister. So does the certificate of rent paid show that you pay rent at the house that you live in for your sister or for some other address? If it shows the address where you lived that your sister owns and shows your sister as your landlord then everything is ok.
If it shows a different address and a different landlord then it was issued to you by mistake and some poor person doesn't have their rental certificate because of the error. So contact whoever sent it to you and let them know they blew it and don't include it on your taxes if that is the case.