How can I check whether a reimbursement has been processed?

In your account, you can check under 'Financial' > 'Special Payments' to see if the reimbursement has been processed in full. It will then be reconciled on the next invoice. Don't want to wait until an automatic new invoice follows? Create an 'interim invoice' yourself. Click on 'Financial' > 'Upcoming invoice' in your account. Here you can see the amount of the upcoming invoice at that time and choose 'Create Invoice'. Now you have created an 'interim' invoice, and you will see it appear in your invoice overview.