The property should be declared in the OPF file

ERROR

ERROR(OPF-014): my-file.epub/OEBPS/Text/file.xhtml(14,32): The property 'svg' should be declared in the OPF file.

Solution

Open content.opf file and find inside manifest tag the declaration of page when error occurred.

On this example find "file.xhtml" 

<item id="file" href="Text/file.xhtml" media-type="application/xhtml+xml">

On this line add the attribute properties="svg"

<item id="file" href="Text/file.xhtml" media-type="application/xhtml+xml" properties="svg">