Some Android phones will process payments faster than others. Try opening Google Pay when you tap to get a faster response. Also, be sure your phone is positioned over the contactless payment logo in the black area below the screen, with the back of your phone touching the reader.
If you don’t get a response from the reader within two or three seconds, try again with your phone in a different position. Depending on what kind of phone you have (and where its antenna is located) you may need to experiment a bit to find the best position to tap your phone. Try to hold your phone still while tapping (that is, don’t move or swipe your phone over the reader).