I just found this thread when looking for Ringlead, just thought I'd say, I did get this working with Ringlead support, in the old version, it's all about the RLMKTO 1 & RLMKTO 2 codes being correct, then Ringlead merges the lead and the contact together, and once it all merges, it goes down to 1. This is an old thread but just thought I'd add that in. Though this is old Ringlead, where as new Ringlead webhook doesn't use the RLMKTO codes at all.
Thanks Luke!