Minecraft check for 25 iron command

Question

I am trying to make a shop to give 1 diamond for 25 iron in 1.13.2. I have the commands "/give @p Minecraft:diamond" and "/clear @p iron 25" though when I click the button again even if you don't have 25 iron it will still give you a diamond. What the command to test to see if someone has 25 iron.

Answer 1

Me intresting too. what the command to see if someone has 25 iron?