Message type: E = Error
Message class:  SD_FREE_GOODS_MSG - Message class for Free Goods maintenance 
Message number: 029
Message text: Free goods category is required.
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The SAP error message SD_FREE_GOODS_MSG029 indicates that a free goods category is required in the sales document you are trying to process. This typically occurs in the context of sales and distribution (SD) when you are attempting to create or modify a sales order that includes free goods.
Cause: The error arises when: The sales order is configured to include free goods, but the system cannot find a valid free goods category. The free goods category is not defined in the pricing procedure or is missing from the sales document. The configuration settings for free goods in the sales document are incomplete or incorrect.
Solution: To resolve this error, you can take the following steps: Check Free Goods Configuration: Go to the transaction code SPRO to access the SAP Customizing Implementation Guide. Navigate to Sales and Distribution > Basic Functions > Free Goods. Ensure that the free goods category is defined correctly in the system. Assign Free Goods Category: In the sales order,
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