According to the docs the proper curl command is;
curl -X GET -H "Authorization: sso-key [API_KEY]:[API_SECRET]" "https://api.ote-godaddy.com/v1/domains/available?domain=example.guru"
Copy the curl above, then click on “Import” > “Raw text” and then paste your curl command in there with your keys, like this;
Then click continue and it should work.
The keys are passed in the header in this format
Authorization: sso-key [API_KEY]:[API_SECRET]
But your screenshot shows the keys without the sso-key prefix.