If you haven’t gone to the settings/or getting started and clicked “edit chat plugin” button, that step is necessary for the chat bubble to show up.
Here are some steps from a relevant troubleshooting process from the help page.
If you had this issue but didn’t find this page in your searches, please let us know. (from: https://www.facebook.com/business/help/789975831794468 )
– Check that you’re running the latest version of the plugin, and the plugin status shows as Activated. You can view the status in the Plugin tab in your WordPress homepage.
– If the Facebook Page the plugin is associated with has age or location restrictions, the plugin will not load for users who fall outside of the allowed age range or location. Guest users who are not logged into Facebook will not see the plugin at all.
– If your WordPress installation is deployed on multiple websites with different domains, you will need to set up the Chat Plugin from the Admin section for each instance of your site, so each domain has access.
Check that you’ve disabled any ad blockers running in your browser.
– If you have other WordPress plugins active in your installation, try deactivating them all temporarily and reactivating the plugins one by one.
To inspect more closely whether the code has been correctly deployed into the site’s source markup, you can view the source and search for a div tag with the class attribute fb-customerchat.
– If the code is present, but the plugin still does not appear, there may be CSS style rules causing the plugin not to render properly. Read the Chat Plugin shows differently than preview section below to troubleshoot.
Thanks