Failed to notify callbackurl
The so-called callbackurl is a security feature in Quickpay. The status (payment was successful or not) of each transaction is always send to the callbackurl.
Please do not rely on the OK-page. Skilled haxors can "cheat" with OK-page and may called the OK-page without necessarily ever conducted a real trade.
One should therefore always use callbackurl.
If you get the error "Failed to notify callbackurl" it will appear in the manager and the transaction be marked with a yellow warning triangle. You should implement your shop system so this yellow warning is avoided.
Server responded with status code "302"
If you get status code of 302, you do not have to do anything and everything is probably OK.302 is a so-called HTTP status code and just means making a redirect to another page.
Server responded with status code "404"
The 404 or Not Found error message is a HTTP standard response code indicating that the client was able to communicate with the server, but the server could not find what was requested.The page you have stated as callbackurl does not exist. You should fix this immediately.
Server responded with status code "500"
HTTP stataus code 500 is a catch-all error generated by your Web server. Basically something has gone wrong, but the server can not be more specific about the error condition in its response to the client. In addition to the 500 error notified back to the client, the Web server should generate some kind of internal error log which gives more details of what went wrong. It is up to the operators of the Web server site to locate and analyse these logs.