To connect your Overstock with eSwap you need to request your Supplier Oasis API username and API password.
It’s likely to use your Supplier Oasis credentials as API username and password.

After getting credentials sign in to your eSwap account, navigate to Available apps -> Overstock, and click on the Install app button. Now give a name that you want to see in eSwap, fill in Supplier Oasis API username and password, and click on Install app.