I don't want to nitpick but ... are you really 'focused' on this? You're a startup with limited resources trying to get a product up and running with commercially-viable feature-set. You're not setup for high availability. You just aren't. Proper HA is very hard and as you climb the '9s' in uptime, you introduce huge amount of complexity, cost, planning and manpower - which is something you haven't done and can't do as a startup and, honestly, it isn't worth to do for a Webhook SaaS.
And that's OK! The nice thing about Webhooks is that nobody runs mission-critical workflows with them because there is an implicit expectation of unreliability. This means that for HA/uptime you just need something reasonable. Your service may not survive an AWS outage (or whatever cloud service or datacenter you're deployed in) or a directed DDOS attack, but if your infrastructure can handle traffic spikes and occasional node going down - you're golden.
That's a fair assessment! We are indeed a startup, and definitely have limited resources. What I meant is that this is one of our top concerns that we constantly think about and deploy (our limited) resources on! We are definitely not where we want to be just yet!
This is something we focus on though, and as part of this focus, we will focus on earning this trust and making it as transparent as we can.