W3C Markup Validation Error

Hi,

I just ran the W3C Markup Validator and it brought up this issue in my blog:-

Error Line 2, Column 167: there is no attribute “prefix”
…ww.addthis.com/help/api-spec” prefix=”og: http://ogp.me/ns# fb: http://ogp.me…

How can I fix this?

Thanks

Neil

https://wordpress.org/plugins/addthis/