When a site owner installs your app, they will grant you permission to collect their site data during the installation flow, which is based on the settings you provide in the Wix Developers Center. You will then receive an authorization code which you will use to request an access token and a refresh token. Then you’ll pass the access token as an authorization header in the API call.
Also, there is a solution that can help you to connect your B2B software with Wix easily. It’s HexaSync – eCommerce platform integration software. HexaSync provides a great number of API methods for managing the data. For example, with their help, you can get the list of orders, products, and customers from Shopify e-stores, update order info, get info about taxes, add and update shipments, etc.