Webhook Cannot Be Verified

Hi. I’m trying to configure the connection to FB and followed FB API Guide in the plugin setting. However, when I’m trying to verify the callback URL with the token, it keeps on saying “The callback URL or verify token couldn’t be validated. Please verify the provided information or try again later.”

Here’s a screenshot of the error: https://snipboard.io/tJEqp0.jpg

I just copied and pasted what the plugin provided. Hoping you can help me get through this.