If you are not using LinkedIn Premium, you must use Mini Cover Letter Invites. But if you are using Premium then in some cases may be advisable to use an INMAIL, in which case, you have to send to FULL

Source: When you see a Job Post of your interest, probably your first reaction will be to run, and click apply bottom or shoot an email attaching your resume. WRONG. You just made a big mistake. Before

Source: Assuming you have sent an excellent Mini Cover Letter within the body of the Invite {300 limit characters}, and got accepted, then you need to continue with the Selling your Case. Why? The Mini