Private key file required

Hi I want to connect my amazon account with a website there is an automatic button through which we can login and register a merchant because the merchant is already registered I am adding keys manually I have added all three keys
Merchant ID
Public Id
Store Id
I have also downloaded a JSON file the problem I am facing is at the Private key. The error comes
“Error: You must add the private key file.”
I am unable to find a private key file. I found this guide
https://developer.amazon.com/docs/amazon-pay-api-v2/manually-generating-key-pairs.html
And when I tried to follow it I am stuck at this step
https://paste.pics/811e2fe3c11ce54946bffb0ab9c11c06
“The key you entered is not valid”
Iam adding a Public key id here.
Thank you
I am copying a Public key as it says but its giving me an error

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