I got the same problem. I already have registered the google api key, but got the error
library(ggmap)
register_google(key = "xxx")
ggmap(get_map(location=c(16.3738,48.2082), zoom=13, scale=2))
#result like this:
Source : https://maps.googleapis.com/maps/api/staticmap?center=48.2082,16.3738&zoom=13&size=640x640&scale=2&maptype=terrain&language=en-EN&key=xxx-NpzDmD5s Error in curl::curl_fetch_memory(url, handle = handle) : Timeout was reached: [maps.googleapis.com] Connection timed out after 10001 milliseconds