Thanks, Greg. Jamie you can do this with FlowBoost Community (i.e. Free) Edition as well.
On the webhook side, adding a lead to an event counter is as simple as
FBCounter.add('event_123/{{Lead.Id}}', '{{Lead.Email Address}}')
The key here (literally) is the Lead ID. Including the email address, first/last name or other metadata about the lead is optional, but keying on the ID is critical for management. (If you keep email dupes in your instance, as some users do, you don't want to confuse two people who share the same email.)
While you can check the difference between the registration cap and the current count while registering the lead, you don't necessarily need to (unless you want to send an internal alert) so the above may be all you need in Marketo itself. To suppress a form/redirect when the cap is exceeded, that's all in the browser:
<script>
function checkRegCount(current){
if (current.count <= {{my.registrationCap}}) {
// call standard MktoForms2.loadForm(), etc.
} else {
// redirect to 'Event Full' page, load a 'Wait List' form, show/hide content, etc.
}
}
</script>
<script src="https://api.figureone.com/fbcounter_v1/counter/event_123/count?cb=checkRegCount&public-api-key=a1b2c...">
</script>
Note I'm using a {{my.token}} to store the registration cap -- very convenient when using Marketo LPs, since you can raise or lower the cap instantly. On a non-Marketo page, you could hard-code the cap in the code (current.count <= 25).
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