Idp Mapping of string to string array

Attempting to figure out how to map a string value from an Idp to a string array on the Okta profile.

I have attempted creating a string array on the Idp profile and then using an expression to add the string to the string array and then mapping that string array but no go. I keep getting an error saying that the output is ‘fx’.

For demonstration purposes let’s assume…

Idp string = idpString
Idp string array = idpStringArray

Okta string array = oktaStringArray

The expression I tried:
Array.add(idpStringArray, idpString) => oktaStringArray

Anyone know how to add a string to an array in the Okta profile?