WordPress Caching Fix: WP Simple Pay "cookie_check_failed" Error

We run a WordPress site with WP Simple Pay for payments. Some customers hit a "rest_cookie_invalid_nonce / cookie_check_failed" error at checkout. The cause is a caching conflict, and I need someone to configure our caching correctly so payment pages are excluded and the error stops. Setup: WP Simple Pay SiteGround Speed Optimiser Asset CleanUp Pro Reference for the issue: https://wpsimplepay.com/doc/rest_cookie_invalid_nonce-cookie-nonce-is-invalid-cookie-check-failed/ Scope: diagnose the conflict, configure cache exclusions across the plugins (and Cloudflare if relevant), confirm the checkout works for logged-out users. Small, well-defined job. Quick turnaround preferred. To apply, tell me briefly how you'd approach the diagnosis.