Can Google Photos on iOS use mobile data connection to back up?

For some reason, I already turned on Mobile Data for Google Photos in iPhone settings, but it still says "Waiting for Wifi" in the app. After I turned on Wifi, and tapped on the backup button, and went to another app, the backup didn't run in the background for the first time. The second time, it did run in the background. Is there a way to make it always back up in the background?