You need this to get it done:
Action DetailsRequirements and how-to articles for LinkedIn's action:
Choose your target audience based on attributes such as location, job experience, interests, etc.
The internal name for your campaign (not visible to the public.)
Sponsored InMail Ad Name
A name for your Sponsored InMail Ad.
The subject line for your InMail message (maximum of 60 characters.)
The main body text for your InMail message (recommended to keep it under 1,000 characters.) You can use custom fields for the user's first and last names.
Landing Page URL
The URL which the user is taken to when they click the call-to-action button. (must begin with http:// or https://)
Call to Action Button Text
The text to be displayed on your call-to-action button (maximum of 20 characters.)
Campaign Manager Account
In order to be able to use LinkedIn's Campaign Manager, you must made an account for it. You need to enter an account name (up to 100 characters including spaces), your currency (which cannot be changed later) and if you wish you can associate a LinkedIn Page with your account, but this is optional (although some ad formats require a Company or Showcase Page to be linked.)
Budget and Bid Type
Choose your budget (either daily or total) and the bid amount. The bid type for Sponsored InMail is cost per send.
Decide how long you want your campaign to run. A starting date is required (either start immediately or schedule a starting date) and you can enter an end date if you wish, or leave it blank for your campaign to run until your budget runs out.
A banner image to be displayed to the right of the InMail message.
File format: .jpeg/.jpg/.png
Resolution: 300 x 250 pixels
Choose the language of your campaign.