Facebook Messenger Callback

Hello, I have created a site that I intend to use as a webhook for Facebook Messenger. However, for some reason on Facebook when I try to verify my callback URL and verify token I get an error:

"The callback URL or verify token couldn't be validated. Please verify the provided information or try again later."

Looking at the access long I can see that my site is receiving a GET request when I access the site, - - [05/Jun/2024:20:03:46 +0000] "GET /webhook HTTP/1.1" 200 4 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/16.2 Safari/605.1.15" "" response-time=0.001

However, when I click the Verify button on Facebook nothing occurs in the access log.

I've been stuck on this for a few hours and not sure why this is happening. The Facebook forums were pretty unhelpful so I thought someone here might have some experience. Thank you

Are you sure you're using the right callback URL?