Connected, but nothing works

Check from the bottom

When a board says it is connected and nothing works, the code is the last place to look. Each check stands on the one under it: steady power as the radio starts, a network on a band the chip has, that network in the scan, the password, a usable signal, an IP address, and a way out through the gateway to a name server. Find the first that fails and fix that one. A check above a broken one proves nothing.

Print the reason

The faults look different on the serial port, if the sketch prints why the board disconnected. A reset as Wi-Fi starts is power: the transmit burst can pull a weak USB cable's voltage down far enough to brown the board out. Reason 201, no access point found, is the band or the name. A wrong password usually shows as a handshake time-out, reason 15 or 204. Reason 200, a beacon time-out, or 212 points at the signal. Print the reason before you change code.

ESP-IDF raises two events, and they are not the same thing. WIFI_EVENT_STA_CONNECTED means the board has joined; IP_EVENT_STA_GOT_IP comes later, once DHCP has handed it an address. Connected without got IP is the address, and no change to the Wi-Fi settings fixes a router whose DHCP server is not answering.

The router's side

Most ESP32s are 2.4 GHz only; the C5 also does 5 GHz. A 2.4 GHz chip never sees a 5 GHz-only network, and fails with 201. Dual-band routers often use one name for both bands: if yours hides 2.4 GHz behind one name, check it is switched on. If the router is on channel 12 or 13, set the board's country, because a board left on the default may miss it. Recent ESP32 software speaks WPA3; if it cannot match the router's security, reason 210 says so. On Arduino, check your core's build.

Past the address

An address and names that do not resolve is a DNS or uplink problem, not a Wi-Fi one and not the board's. A hotel or café network goes one step further: the board joins and has an address, but the network wants a login page the board cannot see.

The code is in the ESP32 book, from station mode; what uses the address is TCP and UDP.

Common mistakes

• Starting with the code. The board has usually already printed what is wrong. Read the serial output and check from power upward first.
• Taking WIFI_EVENT_STA_CONNECTED for online. It means joined. Wait for got IP before opening a socket, and test a name lookup before blaming the board.
• Fixing the second fault first. With two faults, only the lower one shows. Fix it, then check upward again: the next one appears only then.