How to get row count based on other column groups

I need to count the number of dates with which the invoices are made to certain customers in each month

Consider the table named Table1

Branch  Month  Date     Amount
----------------------------------------
 B1     April  01/04/20  10000
 B1     April  14/04/20  13000
 B1     May    01/05/20  25000
 B1     May    14/05/20  23000

I tried the folllowing code

Select 
    Branch, Month, Date, Amount,
    Row_Number() over (partition by Branch order by Month) as rowcount 
from table1

and the result was

Branch  Month  Date      Amount   rowcount
----------------------------------------
 B1     April  01/04/20  10000      1
 B1     April  14/04/20  13000      2
 B1     May    01/05/20  25000      3
 B1     May    14/05/20  23000      4

The result I need should count the column named branch based on column month, the desired result is

Branch  Month  Date      Amount   rowcount
---------------------------------------------
 B1     April  01/04/20  10000     1
 B1     April  14/04/20  13000     2
 B1     May    01/05/20  25000     1
 B1     May    14/05/20  23000     2

Here rowcount is based on both column branch and Month, how can I get this result?

Answer

You need to partition by month. Something like this:

row_number() over (partition by Branch, month order by Month)

Note that month is repeated. An order by is needed in SQL Server, so you need something. Other options are:

row_number() over (partition by Branch, month order by (select null))
row_number() over (partition by Branch, month order by date)

I suspect the last is what you really want.