User has to be an admin of the Linkedin page to grant access.
1. Click on Settings button on the lower left hand corner of your LinkedIn page and click on the Manage Admins.

2. Click Review > Accept.

3. Go to Paid Media Admins tab. Click on Add Paid Media Admin.

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4. Enter <email or person's name>, (owner/admin of the page) tick on the role options below and hit save.