Failed to parse Markdown frontmatter.

Example error messages:
can not read an implicit mapping pair; a colon is missed
unexpected end of the stream within a double quoted scalar
can not read a block mapping entry; a multiline key may not be an implicit key

What went wrong?

Section titled What went wrong?

Astro encountered an error while parsing the frontmatter of your Markdown file. This is often caused by a mistake in the syntax, such as a missing colon or a missing end quote.