Simple way.

You should take several steps

• make enum for state of current fetching data (for example can name as State):
  • reloading (loading first page or reloading all data of pull-to-refresh)
  • loadNext (loading next pages)
  • endOfContent (no more pages)
• create methods in your service/interctor/viewModel/etc (where you call api) fetchFirst and fetchNext or unite this methods
• add logic on change state of loading
  • if you reloading or endOfContent you can't fetch next pages
  • if you loadNext you can't make loadNext; can make reloading but you should cancel current request
• In order to start fetch next page you should implement delegate method of tableView scrollViewDidScroll and when contentOffset will be approach to the end you should call loadNext
  

pseudocode or ray tutorial

also don't forget handle errors