In Pokemon Go, I have 40 Pokeballs but can't seem to use them. Help!

[iMore Question]

I am new to Pokemon Go. I was able to capture Pokemon until I ran out of Pokeballs. I bought more Pokeballs. I now have 40 Pokeballs but now when I tap on the Pokemon, nothing happens.

 

[metllicamilitia]

You don't tap on the Pokémon, you press and hold on the Pokéball and fling it with your finger to throw it.