Do not only use url.QueryEscape(str).

[Altynaisuny]

amazon:
http://docs.developer.amazonservices.com/en_US/dev_guide/DG_QueryString.html
Signature query string:
Percent encode the space character as %20. Do not percent encode the space character as +, as some common encoding schemes do.
url.QueryEscape will encode the space to "+", not "%20".
so you need to use url.PathEscape() first .
such as : apiParams = append(apiParams, key+"="+url.QueryEscape(url.PathEscape(str)))