Invoice/receipt

I recently purchased an app for my school set of ipads through the Apple School Manager account which I have my own bank card set up on. Normally when I do this, I receive an email invoice and I claim my payment back at school as an expense. This time however, I haven't received an invoice or receipt via email and so I cannot claim it as an expense. The information about past purchases on the Apple School manager site isn't enough, I need a receipt or invoice. How can I go about getting one emailed to me?