diff --git a/lib/refrepo/utils.rb b/lib/refrepo/utils.rb
index 47b011df693d169e36bd032be1646acc9336f3cf..35ad5d5303459b6fabf3b99b2ea55e08acabc98d 100644
--- a/lib/refrepo/utils.rb
+++ b/lib/refrepo/utils.rb
@@ -13,6 +13,7 @@ module RefRepo::Utils
       o = { :http_basic_authentication => [conf['username'], conf['password']] }
     else
       o = {}
+      puts "Check the documentation https://www.grid5000.fr/w/TechTeam:Reference_Repository#Credentials and your ~/.grid5000_api.yml file"
     end
     d = URI.open("#{conf['uri']}/#{conf['version']}/#{path}", o).read
     return JSON::parse(d)