Hello Gayathri,
Before answering the v15 solution, I wanted to mentioned Odoo version 16.

Odoo 16 analytic accounting
There is big change in in Odoo 16.
In Odoo 16, there is no analytic tag anymore. So if you are considering using analytic tag in v15, make sure you have analytic account set in analytic tag. Otherwise, once you upgrade to Odoo 16, you might lose analytic tag information.
In v15, the benefit of analytic tag is to allow user to select many analytic accounts at once for each journal item.

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Setting:
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Currently, I setup based on your requirements:
Analytic tag: Branch 1. Set analytic account Branch 1. So if we upgrade to Odoo 16, we will still have Branch 1 information.

Analytic account: ‘Department: Sourcing’

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Workflow:
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1.      Create an invoice with income account, using analytic account: ‘Department : Sourcing’ and analytic tag: Branch 1.

2.      Then in the following financial reports: P&L, GL, TB, you can choose analytic account or analytic tag in order to display the journal entry with journal item analytic account, analytic tag sets.
2.1 P&L set analytic account

2.2   P&L set analytic tag

2.3   GL

2.4 TB