iI have powered the espESP module with 3.3 volt3V of arduinoArduino itself. i
I too used to get the error always untill iuntil I changed my settings to "no line ending" at the bottom of the serial monitor. i
I had kept it to "NL & CR" from other answers that iI read in stackhere, and that was the reason for errors iI suppose. anywayAnyway changing it gave me the AT OK.
You should try that first.