To ensure a seamless QuickBooks configuration when going to production and avoid encountering the error message "There is no sandbox companies found for the user" it's suggested to review the QuickBooks configuration.
Go to Apideck > Configuration > Accounting > QuickBooks
Select the "Production" environment for your integration.
Provide your Oauth Client ID and Secret.
In our QuickBooks Oauth Credentials Guide, you can find all the setup steps for creating your own OAuth app including the answers to the App assessment and compliance questionnaire of QuickBooks.