If you need a reimbursement of your travels you shouldn't get your tickets from Opodo because they will never provide you a simple invoice and added on top they will waste your time. Although they have an option in their website to ask for an invoice and when you request it you will receive a mail that they got your request and now they are dealing with it, they won't. Then you write to the customer service, you will receive same reply. Then you decide to make a complaint to trustpilot. Only then a real person will contact with you just to say they can only give an invoice for the services not including the price of the ticket and they will add for their own amusement "I believe this is not you wanted but this is what we can give".
Then you will try to contact with the airlines they will tell you that you paid the money to Opodo then (logically) Opodo should provide it. But to their kindness they would send you all the documents they have regarding to your ticket but none you can count as invoice.
And because Opodo do not cares if a customer is happy or not about them and because there is not much option for complains I have decided to write here.
And If there is anyone who faced with the same problem and solved, I would be very happy to listen their experiences. though all these took me 3 months and I am not sure now even if I can get a reimbursement from where I work. Opodo basically cost me to lose 200 pounds.. I will never again try to save 20-30 pounds while buying my tickets as in return that cost me much more than that.