Hi Inês Mendes
Here you need to make some changes in item category settings. In standard TAX is billing relevant and it has schedule line category CX with no movement type. You need to make it not relevant for billing here. TAPX is not relevant for billing and you need to make it relevant for billing and activate price on it. In short make all settings in TAPX which are there for TAX and maintain copy control from delivery to billing for TAPX.
Please don't use TAX and TAPX item categories and it would be best if you make their copies and make these changes in copied item categories. Try this and update with your findings.
Thank$
