You don't need to take part in every opportunity. Declining is a normal outcome, and it's more useful to the publisher than letting a pitch expire.
You'll be asked for a reason
Before you submit, you'll pick a reason from a short list — covering things like budget, timing and whether the content fits your current plans.
The publisher is then notified that you've declined.
Why the reason is worth a moment
The reason you choose gives the publisher useful context when considering future opportunities for your brand — for example, whether the issue was timing, budget or the type of content itself.
If you change your mind
A declined pitch can't be reopened. If you'd still like to work with that publisher, the usual route is to set up a campaign and pitch them directly — see What do I need to set up a campaign?
