Why would my app be working perfectly on iOS, but not Android? java.net.ConnectException; refused connection to Firestore; ECONNREFUSED

Question

I'm working on an app that's on both Android and iOS smartphones (available for download on Google Play and Apple App stores). I use Flutter as my SDK, with Google Cloud Firestore being used as my database. My app works perfectly on iOS, but the exact same code just leads to a white screen containing only the static UI elements for my app, without any of the elements built with data from Firestore. I keep getting this same error about a connection exception. Does anyone have any ideas?

W/Firestore(31586):     at libcore.io.IoBridge.connect(IoBridge.java:142)
W/Firestore(31586):     at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:142)
W/Firestore(31586):     at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:390)
W/Firestore(31586):     at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:230)
W/Firestore(31586):     at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:212)
W/Firestore(31586):     at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:436)
W/Firestore(31586):     at java.net.Socket.connect(Socket.java:621)
W/Firestore(31586):     at java.net.Socket.connect(Socket.java:570)
W/Firestore(31586):     at java.net.Socket.<init>(Socket.java:450)
W/Firestore(31586):     at java.net.Socket.<init>(Socket.java:250)
W/Firestore(31586):     at javax.net.DefaultSocketFactory.createSocket(SocketFactory.java:285)
W/Firestore(31586):     at io.grpc.okhttp.OkHttpClientTransport$4.run(OkHttpClientTransport.java:555)
W/Firestore(31586):     at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:123)
W/Firestore(31586):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
W/Firestore(31586):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
W/Firestore(31586):     at java.lang.Thread.run(Thread.java:923)
W/Firestore(31586): Caused by: android.system.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
W/Firestore(31586):     at libcore.io.Linux.connect(Native Method)
W/Firestore(31586):     at libcore.io.ForwardingOs.connect(ForwardingOs.java:94)
W/Firestore(31586):     at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:138)
W/Firestore(31586):     at libcore.io.ForwardingOs.connect(ForwardingOs.java:94)
W/Firestore(31586):     at libcore.io.IoBridge.connectErrno(IoBridge.java:156)
W/Firestore(31586):     at libcore.io.IoBridge.connect(IoBridge.java:134)