You don't need an ISBN to publish an ebook through PublishDrive.
We don't assign any ISBNs to publishers, but publishers can receive PublishDrive’s Unique Identifier (PUI) which is accepted by most retailers.
If you already have an ISBN assigned to your book, you can carry it on and use it in PublishDrive.
If you have an ISBN for the print version of your book, that can only be used for print distribution. You cannot use the ISBN you received for the print version when distributing your ebook: you need to apply for a new ISBN or distribute your ebook without ISBN.