If you are verifying your company through Facebook Business Manager and you discover that the button to start the process is grayed out and not clickable, you can unlock it by following these simple steps:
Step 1: go to the Facebook Developer page (https://developer.facebook.com)
Step 2: click "Get started" in the top right corner
Step 3: complete registration steps by confirming your information
Step 4: click on "Create an app"
Step 5: select Manage Business Integrations> Give your app any name> select that you will use the app for for "Yourself or your own business" app and select the Business Manager account for which you want to unlock the verification button.
Step 6: confirm the creation of the app
Once this is done, the button to start the verification process of your company will be unlocked and you can continue with the sending of the required documentation from the Security Center of your Facebook Business Manager account.