Do I need the ""GenAddRecord"" in 'add (child)' button formula ?

I have put an app in the Exchange called URL Formuals for Dummies.  It helps explain these URL formuals.

I will brerak down your code

URLRoot()  // that means mycompany.quickbase.com

& "db/" // you will see that in almost every Quick Base URL


& [_DBID_ID] // this identifies which table in your app 

& "? //this tells the internet that parameters follow and just deliver the parameters to the website (ie Quick Base)


a=API_GenAddRecordForm  // this is an API to put up and Add Record form.


&dfid=10  /this say to use firm ID# 10 in place of the default form.

&_fid_15=" & URLEncode ([Record ID#]) // this says to preload into field ID the value of Record ID# from the Parent Record that you launched off if.

& "&z=" & Rurl() //   that means that upon save to return to where you launches from instead of displaying the newly created record.

so yes, you need to specify which API you are calling when you call an API.

This piece here

"?a=nwr&

says

NeWRecord

nwr means new record, so its just short form for that particular API

It's probably some legacy code for adding a new record and then they turned it also into a proper looking api.