[Spare_account]

>We were fortunate in that we had a backup payment gateway integration "just in case"

This seems like the key point here. I'm not a software guy or even a payments guy, I'm a network infrastructure engineer.

For anything that we want more than 99% uptime, we put in two of everything, sometimes more. Two separate service providers, ideally coming down different physical paths where practical.

[dexen]

"Treat infrastructure as possible failure points and prepare accordingly" holds just as well for the payment infrastructure. Interesting and fresh perspective, thank you for sharing.

[wting]

It's not possible to increase availability with redundancy in all cases, because not all financial actions are idempotent.

For example, sending money via a banking wire. If the bank goes down, you can't send a second wire through another bank without loss because the first wire is not retractable.

[toss1]

Great practice, specifically determining how much redundancy you need, and making sure it is available. The theme also goes with your acct name quite nicely!