How to generate serial numbers for each foreign key and insert them in a different table?

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SQL-Server-2012

How do I can generate serial no for each refno no and insert them to a different
(table B) .Invoice number will be generate based on Table B( - MAX()+1 from Table B) ? MS SQL 2012.

Table A

packname                            refno
----------------------------------- -----------
Demo 250 Channels                   1
qqq                                 1
qqq                                 3
qqq                                 3
Demo 250 Channels                   1
Demo 250 Channels                   1

Result I want
Table B

packname                            refno      InvoiceNo
----------------------------------- --------------------
Demo 250 Channels                   1                1
qqq                                 1                2
qqq                                 1                3
qqq                                 3                1
Demo 250 Channels                   3                2
Demo 250 Channels                   5                1

What I have tried:

SELECT packname, refno,
ROW_NUMBER() OVER (PARTITION BY refno ORDER BY (SELECT 1)) InvoiceNo
FROM Table1

This process run every day and fetch some record and insert into Table2 so when we insert in table2 first time then its OK, but when we run this on second time then its generate duplicate number