Your BigCommerce API Username & API Token have to be configured in OrderCup to fetch, update orders. If there are changes in these credentials on your BigCommerce Admin side the credentials need to be updated back on OrderCup side.
You can configure the credentials easily with the following steps:
1. Login to your BigCommerce store admin
2. Click the Users link at the top.
3. Click on the Go there now link. (Do not click the Create a User Account button)
4. Now click the Create a Legacy API Account button
5. Enter a Username (eg: ordercup, you can use any). The API Path & API Token are generated automatically.
6. Now, in a separate browser tab, login to your OrderCup account and go to Settings --> Store Details and Copy the Username, API Path (copy only til .com, do not copy /api/v2), API Token on the BigCommerce page to Username, URL, Token respectively on the OrderCup page. Click Save on the OrderCup page. And click Save on the BigCommerce page.
You can always check the API user credentials on the BigCommerce Admin side by clicking the Edit link under the Action column.