Calculation to remove a substring

Hi All,

I am continually getting errors when trying to do a retrieve a section from a text field

I have a text field which is populated with the following lets say the field is @URLCode

https://www.whocareswhatthissays.com/contactus?referralcode=1234

What i want the calculated field to do is only display the 1234 (this 1234 is a variable and can be many different lengths

How do i make it so only the value after the = sign is displayed, and if the text field @URLCode is blank to display nothing

Cheers

Appreciate it.

G