Appian Function product

You should only use the rule! notation if you're referencing an expression rule you've created in the environment. For OOTB functions, you're correct in using fn! or nothing at all. Since product() is a function, this error is correct as you've called it as a rule that may or may not exist in the environment.

I did not use the rule! annotation. I used product(10,2) and it threw that error.

Are you saying product(10,20) is throwing this error but fn!product(10,20) is not?

Correct

Could you provide a code snippet of the relevant area for us to take a look? This is odd behavior that I haven't seen in the past. Is product() being called as part of a looping function, or something more simple like populating an individual field's value?

Here is just a quick test snippet:

{
a!sectionLayout(
label: "Items"&product(10,2),
contents: {
{
a!gridLayout(

no looping function just a straight call from an a!save

Very strange.

When I past this test snippet into the Interface designer of my environment, it renders as expected.

Thank you. I am assuming because we have many rules that contains "product" that is what is causing the problem. I will ask Support to take a look.

Do you have any rules that are just named product?

Not that I could find.

Not that I could find.

This happens if you have a rule with the same name, even if this is deleted in past (probable reason you don't see it now, check deletion log) you will still have this issue.
The only way I know you can work around this in the existing environment now is use a fn! everywhere you are calling the Product function.

This is from a past experience, it might be worth taking it with Appian Support to see if they have got a resolution to this in current time.