metadata-meta-authority-cardinality-error.opf

<?xml version="1.0" encoding="UTF-8"?>
<package xmlns="http://www.idpf.org/2007/opf" version="3.0" unique-identifier="uid"
    xmlns:dc="http://purl.org/dc/elements/1.1/">
    <metadata>
        <dc:title>Title</dc:title>
        <dc:language>en</dc:language>
        <dc:identifier id="uid">NOID</dc:identifier>
        <meta property="dcterms:modified">2019-01-01T12:00:00Z</meta>
        <dc:subject id="subject01">Something</dc:subject>
        <meta refines="#subject01" property="authority">https://example.org/authority</meta>
        <meta refines="#subject01" property="term">something</meta>
        <!-- only one authority is allowed -->
        <meta refines="#subject01" property="authority">https://example.org/otherauthority</meta>
    </metadata>
    <manifest>
        <item id="t001" href="contents.xhtml" properties="nav" media-type="application/xhtml+xml"/>
    </manifest>
    <spine>
        <itemref idref="t001"/>
    </spine>
</package>