IPAM is insane. BYOIP requires IPAM. This makes things even more insane - if you want to manage any BYOIP addresses you need to enable IPAM for all IP addresses (not just BYOIP) in an account.

We tried this at a previous job to manage a pair of /24s and it ended up requiring us to manage _hundreds of thousands_ of rfc1918 IP addresses in IPAM, which cost us something like tens of thousands of dollars per month.

For a pair of /24s.