Test send shows "success" but email never arrives (not inbox, not spam) — Free plan, account has never sent a real campaign

Hi all,

I'm on a Free plan account that hasn't sent a real campaign yet (still building out an email template). Whenever I use the template's Preview & test send feature, the UI shows "Your test message sent successfully" and the underlying request returns a 204 (success). But the email never actually arrives — not in the inbox, not in spam.

What I've already checked:

• Tested with two different recipients: our company domain (Google Workspace) and a personal Gmail address. Neither received anything.
• Audience > Profiles: no profile or suppression record exists for either test recipient, so it's not a list-suppression issue.
• Settings > Domains: our custom sending domain shows "Verified" with all DNS records green (NS, TXT verification, DMARC), but the "Activate" button next to it is greyed out/disabled. Routing type is listed as "Dynamic."
• Campaigns: this account has 0 campaigns ever actually sent (only 1 draft exists).
• Billing overview: Email usage shows 0 of 500 sends used this billing cycle, even after several test sends.
• Billing > Payments & Invoices: no payment method and no billing address on file (Free plan).

My guess is one of these:

1. The account needs a payment method / billing address on file before outbound email actually delivers, even for test sends.
2. The sending domain isn't fully "active" despite showing as Verified.
3. There's some account-level hold/review since no campaign has ever been sent from this account before.

Questions:

1. Does a Free plan account need a payment method and billing address registered before test sends or campaigns will actually deliver?
2. Why would "Activate" be disabled on a domain that's already Verified — is that normal for Dynamic routing, or does something need to be enabled on Klaviyo's side?
3. Is there a first-send review/hold for brand-new accounts that could explain a "success" response with no actual delivery?

Any pointers would be really appreciated — happy to share the account ID / domain via DM if that helps someone look into it.

Thanks!