1. Sign in to your LinkedIn account and go to- Work from the top right corner, followed by Advertise (in the drop-down)
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2. Click on the Create account
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3. Fill in the details like Account name, currency and save your account.
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4. Start creating your ads from Create campaign group
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Also Read-
How to add a user to your LinkedIn ads account
How to create Google ads account
How to add a partner/user in your Google ads account
How to create a Facebook business manager account
How to add a partner/user in your Facebook business manager account