How to access the online version of your campaign
To access the online version of your campaign, go to the Campaigns section, and in the dropdown menu of a selected campaign choose the "View email" option.
In the preview, you will find a link to the web URL version of your email. You can copy the link directly from here or open your campaign in a new tab.
It'll only appear for campaigns that were already sent. Drafts don't have an online version.