When someone submits an expense to your Collective, the admins will get an email notification. The email will show all the details of the expense, like who submitted it, the amount, and the receipt or invoice.
You can also view expenses on Open Collective. Click the link from the email notification, or go to your Collective page and click "View all Expenses".
The decision is up to you as a project. Some projects are informal, and any Core Contributor can approve any expense. Others have a formal decision-making or budgeting process, or only pay expenses for specific things. We advise you to have a discussion with your collaborators and agree on guidelines for approving expenses.
Yes, we recommend you have an expense policy, which will show up at the top of the submit expense page.
When you approve an expense, the submitter will get a notification. The Fiscal Host admin will also be notified. They review the expense and make sure it has a valid receipt or invoice, and then proceed to pay it.
The submitter will be notified that their expense was rejected. We suggest also putting a comment on the expense to explain why it was rejected.