* Create `getPaginatedEndpointIterator` to iterate each page
* Create `waitMs` util, it will replace `slowCallback`
* Make `handleAPIError` async
* Make `isAccountUsingPaypal` async
* Make `attemptInvoiceCollection` async
* Make `attemptInvoicesCollection` async
* Use `await` instead of `new Promise`
* Remove unused callbackified `attemptInvoiceCollection`
* Run `attemptInvoiceCollection` for each page instead of gathering all pages in the beginning
* Add test on fetching multiple pages of invoice
GitOrigin-RevId: 2674b18c6ca5732b873fb2bc71b515909006f93d
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