I could not add sp_BlitzIndex store procedure to SQL Server 2014 version

I cannot successfully add the sp_BlitzIndex store procedure for Microsoft SQL Server 2014 (SP3-CU3-GDR) and earlier versions. I think there is something related to the version. Because I was able to add it for SQL Server 2022 version. Can you help me ? PS: I don't know the exact version. I downloaded it as First Responder Kit a few days ago.