Unable to resolve entity on isComponent with :db/add transaction fact

I have this schema:

{:db/ident       :sentence/id
 :db/valueType   :db.type/string
 :db/unique      :db.unique/identity
 :db/cardinality :db.cardinality/one}
{:db/ident       :sentence/words
 :db/valueType   :db.type/ref
 :db/cardinality :db.cardinality/many
 :db/isComponent true}
{:db/ident       :word/value
 :db/valueType   :db.type/string
 :db/cardinality :db.cardinality/one}

When I transact

(d/transact db [{::sentence/id "one" ::sentence/words [{::word/value "word"}]}])
=> {:db-before {...} :db-after {...} :tx-data [...] :tempids {...}}

However, when I transact

(d/transact db [{::sentence/id "one"}])
=> {:db-before {...} :db-after {...} :tx-data [...] :tempids {...}}
(d/transact db [[:db/add 1234567890 ::sentence/words {::word/value "word"}]])
=> Exception {:cognitect.anomalies/category :cognitect.anomalies/incorrect,
              :cognitect.anomalies/message "Unable to resolve entity: {::word/value \"word\"}"}

Before trying it, I had assumed that nested maps would work both as part of a nested map and in :db/add. Here is the documentation on nested map transactions.

Hopefully this note will help someone else in the future.

Is word value unique? If yes then determine :word/value as unique