Why am I see an error, "contains an unrecognised substitution attribute (OPA-E00403)"?

Environment:

Oracle Intelligent Advisor, Oracle Policy Modeling (OPM)

Resolution:

In reference to it's use within Intelligent Advisor, please note that using the character % should only be used as an attribute susbstitution character and in the event that this occurs within a URL, it is required to be escaped with another % so that you have two % characters together. 

Example:

HTML encoding of URL with spaces you use x%20y for https://site.domain.com/x y/ 

When using it inside an interview, inside a label:  You need x%%20y

Exampe;

https://site.domain.com/x%%20y