You are going to need a genuine Apple receipt proof of purchase of that old an iPad.
Apple does NOT hold receipt records for that long a period.
That is why I always ask/get both paper AND email receipts for any thing I purchase from an Apple Store.
Without a proper receipt for this device, it will remain dead and useless to you.
There is nothing more to be done to get that device working,,now.
Sorry.
You might as well takes this 8-year old iPad back to an Apple Store and have them recycle it and purchase a new iPad model OR purchase something refurbished from the Apple online store OR purchase a newer, used, secondhand iPad online, somewhere.
Sorry.
It's 2021, now.
If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted sources, like other Apple product/device retailers/resellers, some locally or from online, on the Web/Internet, capable of running the latest iPadOS versions.
There are PLENTY of newer, older iPad models that can run the latest, current versions of iPadOS.
If you need OR ONLY able to purchase older, less expensive iPad models, look at older IPads from 2014 and later.
All of these older model iPads below CAN run the latest iPadOS versions and the up and coming iPadOS 15.
2014, 9,7 inch screen iPad Air 2 models
2015, 7.9 inch screen iPad Mini 4 models
2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )
2016, 9.7 inch screen iPad Pro models ( 1st gen Pencil support )
2017, 10.5 inch screen iPad Pro models ( 1st gen Pencil support )
2017, 9.7 inch screen iPad 5th gen models
2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )
2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )
2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )
Get the largest internal data storage model you can afford as NO Apple iOS device has expandable storage.
Sorry & Best of Luck to You!