API Key

SparkPost Settings asks for providing an API key.

In my SparkPost account, I am able to create an API key, but can’t see it (except the first 4 digits).

How do I enter the API key????

I have tried entering only the first 4 digits but in that case, I am getting

Preparing request data
Request headers: Array( [User-Agent] => wordpress-sparkpost/3.0.1 [Content-Type] => application/json [Authorization] => 8096************************************)
Request body: {"recipients":[{"address":{"email":"vivek@csillamvilag.com","header_to":"vivek@csillamvilag.com"}}],"options":{"open_tracking":true,"click_tracking":true,"transactional":true},"content":{"from":{"email":"wordpress@rajsorsolya.csillamvilag.hu","name":"WordPress"},"subject":"SparkPost email test","headers":{"Date":"Fri, 5 May 2017 16:15:42 +0000","Message-ID":"<54bff80a34991244a3975a8913f69c71@rajsorsolya.csillamvilag.hu>","X-Mailer":"PHPMailer 5.2.22 (https:\/\/github.com\/PHPMailer\/PHPMailer)"},"html":"<h3>Hurray!!<\/h3><p>You've got mail! <br\/><br> Regards,<br\/><a href=\"https:\/\/www.sparkpost.com\">SparkPost<\/a> WordPress plugin<\/p>"}}
Making HTTP POST request to https://api.sparkpost.com/api/v1/transmissions
Response received
Response headers: Requests_Utility_CaseInsensitiveDictionary Object( [data:protected] => Array ( [date] => Fri, 05 May 2017 16:15:42 GMT [content-type] => application/json [server] => msys-http [cache-control] => no-cache, no-store ))
Response body: {"errors": [ {"message": "Unauthorized."} ]}
Error in transmission