The posting date must be filled in on each document. SAP Business One fills the system date automatically for users when creating a document. This setting is convenient for most users, but SAP Business One also applies other choices for users when they have any special requirements.
SAP Business One enables you to decide whether to “block documents with earlier posting date,” and whether to “allow future posting date.” Go to Administration > System Initialization > Document Settings, choose General tab and click “block documents with earlier posting date” or “allow future posting date” as needed.
These two options are not selected in the default setting, which means users can add documents with earlier posting date but cannot create documents with future posting date.
If block documents with earlier posting date is selected, users cannot post the document before the posting date in the previous document (of the same type). For example, with a purchase order with a posting date of today, users cannot create a new one with a date earlier than today. However, if the last purchase order was posted on 11/01/2017, then you will be able to post a document with any date after 11/01/2017.
If allow future posting date is selected, users can choose an order date in the future.
If you are interested in changing posting date, please visit change posting date in SAP Business One.