I found my mistake.
I added the decoding function of the example to my single asset.
But I did not understand I should make an asset for each asset name in the decoding function.
When I did this, messages started to come in. In debug, there was no message of rejected messages.
I got this clue from this blog:
In there is the tip:
Asset name is case sensitive! So check asset against the payload conversion function asset name.