I'm currently in the process of developing my first API. This is a private api that will send information back and forth between my two sites, not one that will be open to the public. I'm working on making it as robust as possible, but since this is my first time developing something like this I want to make sure I know about any external "gotchas" before I encounter them.
What elements outside of my control could cause my API calls to fail? I assume I should be worried about things like network connectivity but I've been unable to find a definitive list.