The year was 2084, and the "Great Sync" was supposed to be the pinnacle of human-machine diplomacy.

Protocol Mismatches: In web services, "Handshake" errors often occur when there is a mismatch between HTTP and HTTPS. For example, if a client attempts a standard HTTP connection with a server that strictly expects encrypted HTTPS, the initial response may be interpreted as an invalid or unexpected token.

• Check your code settings. Ensure mySerial.begin(...) matches the module's current configuration.
• Auto-Bauding: Many modules default to "auto-baud" mode. You may need to send a command like AT+IPR=9600 (or 115200) while manually probing at different speeds to lock the module to a specific rate.
• Simulator Tools: If using a tool like Proteus, ensure the virtual terminal and the component properties have the exact same baud rate.

You’re not just debugging a handshake. You’re debugging timing. Somewhere, your device started listening 2 milliseconds too early — catching the tail end of a previous transmission.

Check your power supply. Insufficient voltage to the chip can cause "garbage" data to be sent back, which the computer misinterprets as 0x68. 3. SSL/TLS Mismatches

Part 5: How to Fix It – A Priority Action List

Here is your cheat sheet for resolving the 0x68 error, ranked from most to least likely.

Remember: In serial communication, there’s no magic. Only bits, bauds, and bad handshakes. Now go fix that 0x68.

If you connect a TTL device to an RS-232 port without a level shifter:

Check the Logs: Look at the server-side logs. If the server says "Invalid Request," the client is the problem. If the server log is empty, the traffic isn't even reaching it.