Hello, So do you want to make your physical coin being fundable? If you want to choose (Costom)ATOM wallet first at :
https://cosmos.network/ecosystem/wallets/ I thought you will get mnemonic seed 12 or 24 (then your mnemonic will be private key for open your wallet, you can print them as"character or QR-Code"
If you already trying send ATOM which one says "Invalid Address, make sure you have front address "cosmos1PublicAddress.."
Cosmos (Atom) expanded to other network blockchain like BSC, Ethereum, Polygon, and Cosmos.
You can generated own private key not generated by other member here's. it's not how trust we are at this community, you can do it yourself, as long is easy. I believe community could help and sharing.