Follow the below steps to ensure your page is public:
In your browser, logout of Facebook.
Enter your Facebook business page URL into the browser.
Do you see a Facebook page similar to the image below?
This means your Facebook page is not ‘public’. Follow the steps below to adjust your Facebook settings:
Login as the Facebook business page administrator.
Click on ‘Settings’ > ‘General’ tab.
Make sure your ‘Country Restrictions’ and ‘Age Restrictions’ are set to “Page is visible/shown to everyone”.
Once you’ve updated the settings and removed the restrictions, double-check to make sure the page is now public by logging out of your Facebook page and entering your Facebook URL into the browser again. Tip: you should see your Facebook business page.