# Customer codes

Source: https://developer.avalara.com/erp-integration-guide/transactions/simple-transactions/customer-codes/

The `customerCode` value identifies the customer who is transacting with the company. Because a transaction is legally defined as a transaction between a buyer and a seller, the `customerCode` and `companyCode` values identify the two parties involved in the transaction.

For example, if the transaction type is a `SalesInvoice`, the transaction is deemed to be a sale made by the company identified by `companyCode` sold to the buyer identified by the `customerCode`.

This determination is necessary for our software to handle exemption certificates correctly. In AvaTax, the `customerCode` is used to identify customers who have an exemption in either AvaTax or in Exemption Certificate Management. So, AvaTax requires a `customerCode` field to ensure that exemptions will work correctly when you begin working with certificates.