Error 789 when trying to establish VPN connection from Windows 10 to Netgear V7610

Question

I've been trying to establish a VPN between my computer and this V7610 router for quite some time, and getting error 789 "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer"

I think the modem/router is configured ok, because I can establish a VPN from my iPhone. I've tried to use exactly the same settings, L2TP/IPsec, preshared key. I've enabled the additional Authentication protocols in the Security options. I've edited the registry key AssumeUDPEncapsulationContextOnSendRule. All updates are current, so the dodgy windows update that affected VPN's should not be an issue.

What would be the next step in diagnosing the problem....

Thanks 🙏🙏