To Auto Generate Invoice Number (With +1 Increment)

Hi guys, please help.

Im trying to auto generate my invoice number based on the time of departure and the customer name.

If the customer made purchases on two different dates, the first date will become Invoice Number 1, and the later date will become Invoice Number 2 and so on.
There are multiple customers. The increment in the invoice number is specific to each customer. So, there can be multiple invoice number 1. Each customer will have his own invoice number 1.
There can be multiple purchases from the same customer in a single day, all of which will have the same invoice number if they are on the same date.

Please see my attachment file.


Thanks in advance.

Iwan

This proposal fills in the blank cells in column B
1. Select cells B3:B16
2. Select Find & Select > Go To Special > Blanks
3. Type = then the up arrow then press the Ctrl and Enter keys
The formula for the Invoice No. column is: =IF(COUNTIF($D$3:$D3,D3)<=B3,COUNTIF($D$3:$D3,D3),B3)
Let us know if you have any questions.