To connect eBay, add a new account for it under your login email:
Open the account switcher at the top of the sidebar and select Create another account.

Enter an Account name and, under Sales channel, choose eBay.
Under Billing, choose Add to my current subscription. If your plan covers one sales channel, change to a multi-channel plan first, or choose Bill separately.
Select Create account. Quick Setup opens so you can connect eBay and your accounting software.
