Third-party integrations connect via REST API or webhooks. They require your site to be reachable from external servers. When they break, the cause is often something between them blocking the connection.
Cloudflare: The most common culprit. Firewall rules, bot protection, and security settings block webhook callbacks from payment processors and integration platforms. These look like automated traffic — which is what Cloudflare blocks. Check Cloudflare’s firewall event log. Whitelist specific IP ranges for your payment processor.
Hosting WAFs: ModSecurity, Imunify360, Sucuri — can block POST requests and API calls. Hosting provider can check their security logs for false positives.
REST API key failures: Keys break if the site URL changes (HTTP→HTTPS), the user who generated them is deleted, or a security plugin restricts API access. Check WooCommerce → Settings → Advanced → REST API.