Normally you can download your invoice from your Order page.
But, I have purchased Samsung Galaxy Note 10 Plus almost 2 years back from Samsung online shop (India). I wanted the Invoice copy of that order now, and I could not find any option to download the invoice copy from the portal.
So what I did was created a support ticket, provided my order id and asked for the invoice copy. With in 24 hours I received the Invoice as an email attachment.
Dharmesh Pitroda (Samsung)
Jun 14, 2021, 12:15 GMT+5:30
Thank you for reaching out. This is Dharmesh from Samsung Shop Support.
As requested, please find attached the soft copy of your invoice for order no ( 1*********9 ).
We deeply value your relationship and hope to see you soon on Samsung Shop.
So if you do not see the option to download invoice from your order page on Samsung shop, just create a support ticket, you will receive it.