Calculator cannot use a dot

I'm new to this app and I am trying to build a calculator.
Everything works so far apart from the dot button.
When i try to click it an error pops up.
I'm aware that there is a problem with a procedure i made but I don't know how to fix it.
Can somebody help?

You could use a text JOIN block to add each new digit (or '.') to your number display:

set Number.Text to JOIN (Number.Text, (whatever Button.Text))

For the '.' button, you could add an extra pre-test to avoid adding a second '.' to the number.

When you get a math operation (+-*/) Click, don't attempt math until passing is number tests against both sides of the math operation.