Manual TAX Invoice upload to order page

[TGW_Gunther]

On my shop I create a pro-forma invoice using the standard system. Once the customer paid I manually create a PDF Invoice. As my billing company runs its own invoice number system and invoices. So long story short, I’ve got a metafield on my orders page where I can upload said tax invoice once it is paid. How can I show this metafield on the orders page once the customer logged in and view their order so they can download this tax invoice. Please help. Sure there is a simple liquid script or something. Thank you in advance.