X_NOT_FOUND
Means
no row for that id
Typical cause
stale id, wrong tenant, or already deleted — or a single: true query's GET /_x/query/<name> whose sql matched no row (404; fix: x queries show <name> --json)
Fix
confirm with psql "$DATABASE_URL" -c "select id from <table> limit 5" — x db has no query subcommand