Service providers you depend on will fail, either in catastrophic ways or weird almost-working/most-of-time ways, so emergency incidents are going to happen. It

Service providers you depend on will fail, either in catastrophic ways or weird almost-working/most-of-time ways, so emergency incidents are going to happen. It is just a matter of time and scale. Another thing to consider is that your customer might incorrectly point fingers at you when in reality the problem is at their end. This might be due to incompetence or internal politics. And sometimes the blame is more fuzzy when they increase load on your service many-fold one day and latency spikes, which has knock-on effects on their end. Whatever the cause you might need to spend a lot of time to carefully debug and educate people at your customer to keep that organisation happy with your SaaS. A response time of 30 min 24/7 is going to ruin your life, so charge what you consider an obscene amount for this and plan to hire help to cover it. Consider suggesting a very lax but cheaper SLA to them, they might not care much, maybe it is just a check-box on their end?