I see that you regularly purchase credit packs and license assets that are worth a single credit. You won't have an invoice for each asset but for the credit pack purchases. You can sign into https://account.adobe.com, click on Plans > Order History and see the orders you have placed. Also you received an email confirmation after each credit pack purchase. Unfortunately not all orders will show corresponding invoices in Account Management. I am raising this to our product management team.
You would be able to obtain a copy of your invoices by contacting our customer care team https://helpx.adobe.com/de/contact.html. Click on the chat icon in the lower right portion of the page. If you are unable to see this feature you may need to scroll down before it will appear or set your browser to private or incognito mode.