Eligibility says Connect or Check Alerts Panel

Connect

Your Amazon store isn't connected, so Plug Seller can't ask Amazon for you. Connect it in Settings > Store Connect (how). Lists show this as Connect store, and Plug Picks shows Eligibility n/a.

Check Alerts Panel

Amazon didn't answer this time. Open the Alerts panel and press Refresh on the Eligible to sell line to ask again. Lists show this as Eligibility unknown.

Amazon access was revoked

If Store Connect shows Amazon access was revoked, press Reconnect and approve Plug Seller again on Amazon's page.