Wow, with a 500,000,000 user base. I could speculate that 1/10,000 actually are active and use the API.
So let’s say 50,000 use the API daily. Some big companies probably make upwards of 100,000 while smaller only around 10.
Let’s say 25,000 requests average per. [ probably too high ]
Equaling 1,250,000,000 per day.
But as Foxabilo said it can only be estimated.