Problem with blocking IPv6 address

I’m having difficulty getting an IPv6 address to work on the “Backend Block List”. The address in question is 2604:a880:400:d0::34:5001 The CIDR shows up as 2604:A880::/32 . I’ve tried adding the address in that CIDR form and also as 2604:a880:0000:0000:0000:0000:0000:0000/32. But it’s still not blocked – that address still gets through. Should I specify it a different way?