The connection
Settings under Profile has a Publishing row. Flip it and LinkedIn's consent screen asks for three things: to know who you are, your name and profile, and permission to post on your behalf, the scope LinkedIn calls w_member_social. That is LinkedIn's sanctioned route for an app to post as a member, and nothing about it involves your password or a browser session.
LinkedIn issues member tokens that last about sixty days and, on the self-serve tier, no refresh token. When yours is near its end the row in Settings says so, and flipping it on again is the whole fix. If it has expired when a scheduled slot arrives, the post stays scheduled on your board for you to post by hand rather than failing silently.
Two ways out, both after you approve
Open any post in the drawer, read it, edit it. Then either press Post to LinkedIn now, which publishes it and hands back the live link, or give it a slot. The scheduler runs every fifteen minutes and publishes each post whose status is Scheduled and whose time has come. A draft, and even a post you marked Ready, never goes out on its own; Scheduled is the deliberate opt-in state, and moving a post into it is the approval.
A post can carry text alone, one image, one PDF document, which is how a carousel ships, or one video. Sonar uploads the file to LinkedIn and attaches it; the post you previewed is the post that appears. X works the same way through its own connection, and a take longer than X allows publishes as a native thread.
The first comment, the one thing LinkedIn will not let an app do
Many founders put the link or the call to action in the first comment. LinkedIn's self-serve API tier does not allow an app to create that comment on your behalf; Sonar tried it live and LinkedIn refused. So when a post carries a first comment, Sonar publishes the post, copies the comment to your clipboard, and tells you: open the post, paste it, done. A comment on a scheduled post stays with the post in Sonar for you to paste after it goes live. This changes if LinkedIn grants Sonar its Community Management access, and the code already does the right thing the day it does.
What it will not do
Sonar never publishes a draft, never posts anything you have not scheduled or pressed Post on, and never touches your profile beyond posting. It does not reshare other people's posts for you, because LinkedIn's API gates that behind a tier Sonar does not hold, and it cannot comment on other people's posts for you, for the same reason; when you ask for a comment on someone's post, Sonar writes it in your voice and copies it to your clipboard. The Sonar for LinkedIn Chrome extension reads your own analytics page and performs no action at all.
And when a subscription ends, scheduled posts stop going out on their own and wait on your board. Nothing is deleted, and subscribing again resumes the schedule.