Minecraft: Unable to summon entry?

I wanted to spawn fish in Minecraft in the creative, but I can't get it. Nothing comes out of the eggs and "Unable to summon entery" appears in the console. Unfortunately Minecraft does not tell me why it is not possible…

As it is quite clear if you enter the [pos] above the blue marked! So maybe it would be useful to specify a position when asked for one!

Write / summon minecraft: tropical_fish ~ ~ ~

That should work, if not answer here simply. To explain: The "~" stand for the x, y and z coordinates you are currently in.

Alternatively (but a bit harder) you can also type the coordinates as numbers. You can read off your coordinates when you press F3. In each case the number which stands at x, y and z. I recommend you as a beginner but the first method with the ~, which I have written above!

Thanks, was with me the config of a plugin. Whether I forgot the position I can't say, the spawner go again.