Missing content attribute: type

If the "src" attribute is present, the "type" attribute SHOULD be provided and MUST be a MIME media type, rather than "text", "html", or "xhtml". The value is advisory; that is to say, when the corresponding URI (mapped from an IRI, if necessary), is dereferenced, if the server providing that content also provides a media type, the server-provided media type is authoritative.

This may just be a typo. Element names are case-sensitive; make sure you're using the right case.

Otherwise, insert the media type (example: audio/mpeg) of the content as the value of the type attribute.