Hi, I'm having an Australian passport. Can I apply for VOAi n xiamen? And can I travel to shanghai

You can apply for VOA in Xiamen, but you cannot visit Shanghai with this visa. Also, you should have in mind that, in order to be eligible for Xiamen VOA, you have to arrive in Xiamen by a nonstop flight that will not have any additional landing in mainland China. Also, you have to depart from China on a nonstop flight that will not have any additional landing within mainland China.

If I may suggest you, I would suggest you the following itinerary:

Take a flight from some country or eligible territory, for example Australia or Hong Kong and fly into Xiamen using 144 hour visa free transit. After Xiamen, fly to Taiwan. From Taiwan fly to Shanghai, again based on 144 hour visa free transit and from Shanghai return to Australia. So,

Australia - Xiamen (144 hour visa free transit) - Taiwan/ Hong Kong - Shanghai (144 hour visa free transit) - Australia

When using 144 hour visa free transit it is important to know that the immediate points before and after your mainland Chinese destination have to be in two different countries or eligible territories (eligible territories are Hong Kong, Taiwan and Macau).