VOA for Xiamen

Since you are a German citizens and your itinerary will be:

Laos - Xiamen - Thailand

You can be eligible for 144 hour visa free transit. Anyway, there are no direct flights from Laos to Xiamen, so we have a problem here.

By the way, you should definitely not to try to obtain a VOA by arriving on a plane because you will not be allowed to board the plane in the country from where you will depart to Xiamen. There are several examples where passengers willing to apply for Xiamen VOA were denied boarding even in Hong Kong!

In reality, if you find an eligible itinerary for your Xiamen trip that should look like this:

Country A - Xiamen (China = country B) - Country C

You can use 144 hour visa free transit and if you cannot create such an itinerary, you will have to obtain a Chinese tourist (L) visa in advance!