Since I don't know your level of expertise, I'll start by saying that a couple of simple formulas will accomplish your goal. Let's call your data entry sheet something creative such as Data Entry.
In your Invoice sheet you would use simple formulas such as ='Data Entry'!A1. The cell that contains that formula will always match whatever is in DataEntry!A1
If you are looking for something more sophisticated, such as a macro, then you have a couple of options:
1 - The data transfer could be triggered automatically/immediately by the entry of data into the Quantity cell on the Data Entry sheet. This method would not allow for user review, it would just transfer the data.
2 - The transfer could be triggered by a "button" once the data has been entered and reviewed by the user.
In either case, we are going to need more information before any working code could be written. Since the VBA code has to be very specific about where it is getting the data from and where the data should be placed, we will need more detail than "The Invoice will start in line 18 ".
This is an example of what the automatic code might look like. As soon as data is entered in D1, A1:D1 will be copied to Invoice!A18:D18
Private Sub Worksheet_Change(ByVal Target As Range)
'Determine if the Quantity cell (D1) has been changed
If Target.Address = "$D$1" Then
'If Yes, Copy A1:D1 to Invoice Sheet A18:D18
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