Your DKIM signature still says klaviyomail.com
Out of the box, Klaviyo sends from its shared domain, so DKIM signs klaviyomail.com and Gmail shows "via klaviyomail.com" next to your brand name. That breaks DMARC alignment, and since the February 2024 Google and Yahoo rules, anyone sending 5,000+ emails a day to Gmail must send DMARC-aligned mail. Klaviyo's own docs call a branded sending domain a requirement for bulk senders. Set one up under Settings > Domains, then confirm the DKIM d= domain on a live send.