You can transfer rental order costs to the project before posting the invoice. Set Transfer to project to Yes, and then use the Transfer to project button on the Rental order > Invoice page.

This action generates a project journal and posts the rental costs to the project. You can run it in batch or trigger it manually.

On the Posting invoice page, define the calculation date and other parameters. After you click OK, the system generates the project hour journal and allocates all rental costs—including insurance, transport, and warranty—based on item categories.

Check the results in: Project > Manage > Posted project transactions.