Wait for some time and see if the download starts. If the app you are downloading is large, then Play Store may be simply taking some time to prepare for the download.
Here is what you need to do when you can’t download apps from Play Store: Solution 1: Wait For Some Time
How To Fix Play Store “Waiting For Download” Issue? Below, I have mentioned some troubleshooting methods that can fix this issue. These are some of the primary causes of this issue. But, there are various reasons why it may get stuck on this message the download never begins. Normally, the download should start instantly after this message. The “Waiting For Download” message always appears before a download starts on the Play Store.