Solved
WooCommerce integration doesn't work with "Simple JWT Authentication" enabled
Our WooCommerce store requires Simple JWT Authentication plugin (https://github.com/jonathan-dejong/simple-jwt-authentication), but the Klaviyo integration doesn’t work when that plugin is enabled. If I temporarily deactivate JWT, I can connect to Klaviyo but after enabling the JWT plugin Klaviyo shows error message “Klaviyo is no longer authorized to connect to WooCommerce.”
Is there any way to fix this? Other third party integrations work with JWT enabled.