Bitrix24 how to subtract a percentage from the amount?

Question

Bitrix24

In BP, you need to subtract a certain amount of interest from the amount of money? For some reason, this "code" does not work
"= {{Amount}} - 20%" and does not calculate interest at all. Maybe I'm not doing something right?

Answer 1

Here are a bunch of examples: https://helpdesk.bitrix24.ru/open/5428897/
For example, for Activity Log it will look like this:
{{={=Variable:sum}*0.8}}