If your subscription has ended, the account owner can subscribe again and carry on with the same Doorkeep account.
Steps
Sign in as the account owner. Once a subscription has ended, Doorkeep shows a page that says so, with a button to subscribe.
Choose a plan and complete checkout through Stripe.
Once payment is confirmed, your account is active again.
What to expect
Re-subscribing reactivates the same account. It doesn't create a new one or start your setup over. For how long call data is kept, see Fair Housing, call recording, and your data.
While your subscription was ended, callers heard that your number was no longer in service. Once your subscription is active again, Doorkeep starts answering your number again automatically, with your settings and call lists as you left them.
Right after checkout there can be a short delay while the payment confirmation syncs. If your account still shows as inactive for a moment, refresh the page.
Only the account owner can re-subscribe. Team members see the same page but can't check out.
If you cancelled but you're still inside your paid period, you don't need to re-subscribe yet. You already have access until the end date shown on Settings → Account.