NOTE: This works. We have just tested it.

Hi Just went through this. Facebook support was very unhelpful honestly. This is the workaround that worked for me

1. Make sure you have completed your business information on the settings -> About section of the business manager page
2. Turn on 2-factor authorisation for your admin users
3. If the option still doesn't appear - go to the facebook developer page and create an app - https://developers.facebook.com/apps/
4. Associate the new app with your Facebook Business Page
5. In your App dashboard - go to settings and basic and scroll down to business verificatio
6. Click on verify here - for some absurd reason it works! - you will need to upload tax documents etc to verify

Hope this helps

Facebook verify my business button grayed out - how to Enable?

Source: https://developers.facebook.com/community/threads/1010572709333176/