Hover over the banner you want to publish and click Embed icon:
Publish Modal will show up. Choose Ad Network: Google AdManager (GDN).
Click Copy To Clipboard button to copy the embed code into the clipboard:
Now you need to go to Google AdManager to import your banner in ad campaign.
On Delivery menu click Creatives from the left sidebar:
Click Add Creatives:
Select Custom creative type:
Html type Standard, Code snippet - paste embed code from Onlymega, Click-through URL - landing page url, Target ad unit size - size of your banner.
Click Save Creative: