Hello,
As per the documentation only two servers (www.dyndns.org and www.ddo.jp.) are right now available to be configured for DDNS settings on SRX as DDNS servers.
Hence you would not be able to configure custom DDNS servers like Google as they are not supported as of yet.
Please try and reach out to your Accounts team to open an Enhancenment Request (ER) with Juniper to get this feature on SRX.
Thanks,
Pulkit Bhandari
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