Facebook API - The URL couldn't be validated. Callback verification failed with the following errors



Was trying to setup FB messenger webhook with a strong verify token. Somewhat like this: o\/ERviEE\/vt0|<E|\|

set token

The same is been verified in the code:

req.query['hub.verify_token'] === 'o\/ERviEE\/vt0|<E|\|'

However, the value received from FB is: o\\/ERviEE\\/vt0|<E|\\|

get token

This is strange. There seems to be no document reference as such which talks about how Facebook escapes special characters for verify tokens or alike. Not sure if this happens for other entities as well.

Conclusion: need to be a little bit cautious when using special characters for verify tokens.