Click on the "+" next to Products in the left side. Find the Messenger section and click the Set Up button.

Scroll down to the section "Access Tokens" and click Add or Remove Pages. You'll get a pop-up with all the Pages you are admin of, and you then choose which Page(s) you want to connect to Dixa. 

After connecting your Page(s), scroll down to the Webhooks section and click Add callback URL. 

Copy the Callback URL and Verify Token from Dixa,

and paste them into the fields in Facebook. 

Afterwards you click Add submissions and check the box Messages

Finally, you click Add to Submission in the section called "App Review for Messenger" and you make the app public in the top bar. 

The next step is adding the Facebook Page to Dixa.