score/boost with nested items/portable text

[struct78]

I'm trying to use score/boost on nested documents, however I get the message:

score() function received unexpected expression

This is the query that fails:

*[_type in ["pageFaq", "pageContact", "pageFlexible", "pageGeneric", "article"] && ([
          title,
          description,
          pt::text(sections[].list[].answer[])
        ] match $terms)] {
          _score, 
          _createdAt, 
          _id, 
          _type, 
          title, 
          slug { 
            current 
          }
        } | score(
          boost(title match $terms, 5),
          boost(pt::text(description) match $terms, 3),
          boost(pt::text(sections[].list[].answer[]) match $terms, 1), // <-- This line throws the error
        ) 

I've also tried using:

boost(pt::text(sections[].list[].answer[]) match $terms, 1)
boost(pt::text(sections[].list[].answer) match $terms, 1)
boost(pt::text(sections.list.answer) match $terms, 1)

The latter doesn't throw an error, but at the same time it doesn't return a score so I assume it's not working either.