On the Payment Details tab, you can provide information about cash register and documents linked to the payment. 
The "Cash Payment (create)" form. The Payment Details tab
In the Cash Register field, select a cash register to which the funds will be transferred.
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 the 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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There is a switch for changing the display mode which is located to the right on the tab, Table Mode. Use Table mode to apply the payment amount to multiple planning documents and projects. You can add documents one by one to the list in the table (refer to Table mode screenshot below). 
The "Cash Payment (create)" form. The Payment Details tab in table mode
If the payment amount was split, make sure that the sum in the Payment Amount column is equal to the amount in the Total field under the table.
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