use Rails.application.secret_key_base

lib/json_web_token.rb

@@ -4,10 +4,10 @@ module JsonWebToken
   module_function
 
   def encode(payload)
-    JWT.encode(payload, Rails.application.credentials.secret_key_base)
+    JWT.encode(payload, Rails.application.secret_key_base)
   end
 
   def decode(token)
-    JWT.decode(token, Rails.application.credentials.secret_key_base)[0]
+    JWT.decode(token, Rails.application.secret_key_base)[0]
   end
 end