Validation field question

Hi all, I would like to create a text field, or even a different one, that can be validated with respect to an expected value.
Example:
Correct field value as expected value = Promo
I created a text field and used validation with CB Code Field
In validation I wrote the following code but it doesn't work
Can you help me get the result I'm looking for?
Thanks for the support

Should be able to just use normal REGEXP validation for that since the word is static. Example as follows.

Parameters > Validation
Validation Rule: Custom REGEXP Validation
Custom REGEXP Validation: /promo/

As for why your code doesn't work it's because that's not valid PHP. Sorry, I cannot help you with custom coding without a business membership .

Thank you very much!

I noticed that it only works well if the field is required.
If the field is not set as mandatory then it considers it valid even if left empty and therefore the validation has no effect.
 
These are the settings
 
Thanks for the support

A field not marked required is optional so of course it skips the validation if left empty. If you want them to always supply a value be sure to mark it required.