Thumbnail image: Recommended size 1200×627 (Aspect ratio 1.91:1)
Brand logo: 1:1 ratio
Long headline: 50 character max (use long description)
Short headline: 25 character max - required field, though it won't display on Sharethrough inventory
Long body text: 140 character description (use long body text)
Short body text: 90 character description - required field, though it won't display on Sharethrough inventory
Call to action : required field, but not supported.
Additional information may be found on the DBM site here.