On the Payment Details tab, you can provide information about documents associated with the cash payment, taxation details, and information about the exchange rates used for the document. 
The "Cash Payment (create)" form. The Payment Details tab in single-row mode
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In the Document field, select a customer document that will be paid with this payment.
In the Order field, specify a purchase order to which this cash payment is related.
In the Proforma Invoice field, specify an invoice received related to the cash payment.
The Planning Document field is available if the Use a payment calendar option is selected on the Administration > Settings > Cash Management form. The field is auto- populated in case when the payment is based on a Money Transfer (Plan) or Money Payment (Plan) document.
If the Project Costing functionality is enabled in the application on the Administration > Settings > General Settings form, you can link a cash payment with a related project which you can select in the Project field (to find a project, start typing its name or code in the field).
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To add a document, click the Add button on the table toolbar. As you add documents, the columns are populated. 
The "Cash Payment (create)" form. The Payment Details tab.Table mode
In the Payment Amount column, specify how the payment amount is splitted split between documents.
Make sure that the sum in the Payment Amount column is equal to the amount in the Total field under the table.If the amount was applied to multiple planning documents and projects, make sure that the sum in the Payment Amount column is equal to the amount in the Total field under the table.