Connecting JBL Flip 3 and Flip 4

Hello. I have both a JBL Flip 3 and a JBL Flip 4. I also have the JBL Connect app (but can't find any JBL Connect+ app, which I keep reading about). I can Bluetooth pair both speakers to my Google Pixel, but I can't pair them simultaneously. When I press the connect button on the 4, it stays solid white. On the 3, the connect button is flashing white. I've upgraded the firmware for the 3 to match the 4. I don't know how to connect them in stereo format. Any suggestions?