With the update to our new invoice detail page, we've removed the feature to VOID invoices. Please check out our support blog for more information about this link:
Currently, if an invoice must be VOIDed, you will need to contact support in order to do so. In most scenarios, and invoice will not need to be voided and there are options on the invoice page to help you with this. For all other issues, please contact support to help with this function.