Hi,

To link an expense to a specific project in Odoo, you need to use Analytic Accounts. First, enable Analytic Accounting in the Accounting app settings. Then, in the Project app, either create a new Analytic Account or select an existing one for the project you want to link expenses to.

When creating an expense in the Expenses app, find the Analytic Account field and select the Analytic Account associated with your project. By linking the expense to the project's Analytic Account, Odoo can track all income and expenses related to that project, allowing you to generate project profitability reports.

Remember to also link the expense to the relevant sales order if you need to bill the expense back to the customer. Ensure that both the Project and Accounting apps are installed for accurate project tracking.

Reference:-

* https://www.cybrosys.com/blog/how-to-track-the-profitability-of-your-project-using-analytic-accounting-in-odoo-17

Hope it helps