DIAGNOSIS This is almost always a 2.4GHz vs. 5GHz network issue. The S7 only connects to 2.4GHz networks, and many modern routers broadcast both under the same name, which confuses the robot.
FIX 1) Go into your router's settings (usually via a web browser) and temporarily create a separate, uniquely named network that is 2.4GHz ONLY. 2) Disable any "band steering" or "smart connect" features that automatically switch devices between bands. 3) On your phone, forget your home wifi and connect to this new 2.4GHz-only network. 4) Now try the Roborock app setup process again. It should find the robot and connect smoothly. After setup, you can reconnect your phone to your main network; the robot will stay on the 2.4GHz one.
IF THAT DIDN'T WORK The robot's wifi antenna might be struggling with distance or interference. Move the dock and your router closer together for the initial setup, avoiding thick walls or microwave ovens in between.
HEADS UP Some mesh network systems can also cause problems. If you have one, try connecting the robot to the main router's signal, not a satellite node, for the initial pairing. The robot's wifi chip isn't the most powerful, so it needs a strong, simple signal to handshake.