verifyDKIMSignature domain parser misses subdomains

[jp4g]

Take this header field from uber.com:

DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mgt.uber.com; q=dns/txt; s=smtp; t=1728139902; x=1728147102;
 h=Content-Transfer-Encoding: Content-Type: Message-ID: To: To: From: From: Subject: Subject: Mime-Version: Date: Sender: Sender: X-Feedback-Id;
 bh=heSKCLZjKeGc6oRUgGWZ/JnxHzrkVhg6mdIo4v4xijM=;
 b=bRD9ePjQupfNXkcMuBQC/ntOoeN612yIrs5BMEZ82yX4+NQh/Nw+tei5CAlx571fPwX6Nfbvtil8isUOsT5aaN3eUBBDIlTGQix5ndo4UtNuyO45AU3/S3M5DX0j6Ktdiu7aq+kyX0/WxU9dy4JjVhW1xUj71VMzoqMh/30o8FQ=

If I don't specify a domain (i.e. verifyDKIMSignature(rawEmail) it will error with DKIM signature not found for domain uber.com

but if I specify the subdomain manually (i.e. verifyDKIMSignature(rawEmail, "mgt.uber.com") it works fine!