Looking at your account in the API, you show as owning Heresy but not Revenant. The Onslaught: Salvation activity requires the Revenant pass, but players are able to access it once as part of the introduction quest line. It looks like you may be mistaking the activity though, your recent activity shows you doing the Vanguard Ops variant of Onslaught that was added with Into The Light, rather than it being the seasonal version listed in The Last City.