GigSpace asks you to re-confirm each booking twice: once in the week before the gig, and again on the morning of it. Each one is a single tap.
It exists because the worst thing that happens in this business is a venue with no act at eight o'clock and nobody knowing until then. Two taps prevent most of it.
If you don't confirm in time, the agency is told, and GigSpace may cancel your booking and offer the gig to someone on the agency's backup list. You'll be notified if that happens.
Confirming means you intend to be there. If something changes after you've confirmed, cancel through the app straight away; that's far better than not confirming and letting it lapse.
Check-in prompts can't be muted. That's on purpose.