Merge two xml files based on key field - xslt

Question

I have requirement two merge two xml files. Based on the key field in the files I want to merge entire content of the xml 1 to xml 2.
Could you please help me to achieve this scenario.
I have tried this xslt but I am getting below error.
"a sequence of more than one item is not allowed as the first argument of fn:parse-xml()"
XSLT code.
<xsl:stylesheet version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" indent="yes" />
<xsl:mode on-no-match="shallow-copy" />
<xsl:param name="XML1" />
<xsl:variable name="details-doc" select="parse-xml($XML1)" />
<xsl:template match="Key">
<xsl:copy-of select="." />
<xsl:variable name="Key" select="string(.)" />
<xsl:copy-of select="$details-doc/Record/Detail[Key = $Key]" />
</xsl:template>
</xsl:stylesheet>
XML1.
<Record>
<Detail>
<Key>1</Key>
<Place>Ocean</Place>
<City>Urban</City>
</Detail>
<Detail>
<Key>2</Key>
<Place>Road</Place>
<City>Rural</City>
</Detail>
<Detail>
<Key>3</Key>
<Place>Plane</Place>
<City>Semiurban</City>
</Detail>
</Record>
XML2
<Record>
<Contact>
<Key>1</Key>
<Name>Jack</Name>
</Contact>
<Contact>
<Key>2</Key>
<Name>Ethan</Name>
</Contact>
<Contact>
<Key>3</Key>
<Name>Ron</Name>
</Contact>
</Record>
And the expected output.
<Record>
<Contact>
<Key>1</Key>
<Name>Jack</Name>
<Place>Ocean</Place>
<City>Urban</City>
</Contact>
<Contact>
<Key>2</Key>
<Name>Ethan</Name>
<Place>Road</Place>
<City>Rural</City>
</Contact>
<Contact>
<Key>3</Key>
<Name>Ron</Name>
<Place>Plane</Place>
<City>Semiurban</City>
</Contact>
</Record>