In the settings for AMP pages, you can choose which social sharing buttons appear on each post. The default setting includes Facebook, but this requires a Facebook App ID to be populated in the associated text box. If you do not populate this, sharing is broken on the website. Perhaps a warning or error could be generated if you try to build the website when Facebook sharing setting is on but the App ID is missing.
We will consider to prepare some area in Publii which will detect such issues, as there can be more similar problems and it is worth to have some common place for them with explanation how to solve it.
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