update data purging, re-enable channel selection

README.md

@@ -169,7 +169,7 @@ The dashboard provides several tabs:
 
 1. Navigate to the **Messages** tab
 2. Type your message in the text field
-3. Select the channel (0-7)
+3. Choose a device to send **From**
 4. Click **Send**
 
 Messages will be broadcast to the mesh network via MQTT.
@@ -269,6 +269,12 @@ Log level can be configured with `LOG_LEVEL` in `.env` (debug, info, warn, error
 3. Check that there is active mesh traffic on the topic
 4. Review logs for any error messages
 
+### Messages sent over MQTT aren't sent over the radio
+
+1. Ensure the sending radio (node) has a channel called "mqtt"
+2. Ensure the node has Uplink and Downlink enabled on both the default channel (LongFast, etc) and the mqtt channel
+3. Ensure the node's setting under LoRa is "Ok to MQTT"
+
 ### Database errors
 
 1. Ensure the `data/` directory is writable