Send information within Quickbase to an external URL

is the custom code page HTML or a JS page that's executed?

if it's HTML it can be passed as a parameter... if you simply have JS executing on page QB has a global variable called kRid... it is the record ID of the current page.

for JS code pages I generally go something like:

const RecID = kRid;

and then I can use RecID anywhere in my JS code...