Hello @Lourdine Charles,
Thank you for sharing your question with the Klaviyo Community.
I recommend trying some of the solutions outlined in the topic below:
On a high-level, typically the issue behind the error is either a firewall, the WordPress plug-in or another plug-in interfering with the API. If you are unable to resolve using the steps in that thread I recommend taking the following steps:
- Delete the Klaviyo plugin in your store
- Delete the current REST API key/secret combination
- Re-install the plugin
- Create a new API key/secret and use this to reset the integration
Attaching the installation guide here as well.
Thanks and have a wonderful weekend.