Image dimension: 1200x627
Image file size: 5MB
Image format: JPG (JPEG), PNG and GIF (animated GIFs not supported)
Landing page URL: (with UTM if required)
URLs longer than 23 characters are shortened by the LinkedIn
Introductory text: 150 characters
Title text: 70 characters
Description: 100 characters
Reference: linkedin.com/help/lms/topics/8154/8155/ad-specs-guidelines