How to fix XHTML errors?

Hello,

Installed Reveal Discount Code plugin for my site, and getting bellow errors while checking in Markup Validation Service.

1) document type does not allow element “div” here; missing one of “object”, “applet”, “map”, “iframe”, “button”, “ins”, “del” start-tag

2) there is no attribute “data-id”

3) there is no attribute “data-code”

For more information check out https://validator.w3.org/check?uri=http%3A%2F%2Fwww.amplecodes.com%2Ftomato-ink-coupon-codes%2F&charset=%28detect+automatically%29&doctype=Inline&group=0&user-agent=W3C_Validator%2F1.3+http%3A%2F%2Fvalidator.w3.org%2Fservices

Please let me know how to fix these issues.

Thanks