Unable to choose a nickname [duplicate]

I am unable to pick a nickname for my trainer. When I use names like Ash, Millby, or anything else, the game says that it is not availible. What should my nickname be then?

Solution 1:

Its just your username in game. If it is already taken you can't use it. Try adding some numbers or characters. Like Ash1901! or Millby753.

Solution 2:

Your nickname must be unique among all Pokemon Go players worldwide. You can assume that a name like Ash (or any other official character from the Pokemon franchise) was already taken ages ago. That means you need to make up a more creative name.