You don’t have to register an IPv6 IP for access. The whitelist functionality provided in the API registration is only really useful if you are trying to protect your API key if you are using a browser-run Javascript client. See
At the moment we do not support IPv6 whitelisting as complete end-to-end IPv6 infrastructure is rare, and we have always found that browser based Javascript accesses to our API do not come from IPv6 only hosts (or at least, we always get an IPv4 address).
Hope that helps.