Pass value to your custom code page

I setup the the user defined variable required to run scripts off of formula URL field button click

I am currently using:

var dbid = "xxxxxx";
 
var promise = $.post(dbid, {
  act: "API_GetRecordInfo",
  rid: "6400",
});

$.when(promise).then(function(xml) {
  console.dirxml(xml);
  console.log($("errcode", response).text());
});

My issue is that the record ID I have there is hard coded. I would like to pass the record ID of the record I am inside to the code page, to run GetRecordInfo for the record I am on. Where can I read to learn how to do this or can I have some guidance?