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The required field is Entity.
The "Tax Transaction (create)" form. The Main tab
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In the Entity field, select your company's entity for which this document is being prepared. The Entity field is available if the Multi-Company Accounting option is selected on: Administration > Settings > General Settings. You can select your personal default entity to appear in documents; for this, refer to Personal Settings. If you have not selected your default entity, the entity defined first will be used as the system default value.
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For descriptions of other buttons, see Document Toolbar.