I’m having the same problem on a Mega 2560 with HC-05 module
Please don’t add on a “Me too” issue into others old topics. I moved your post into your own current topic.
One possibility of that error is incorrect BAUD rate for setup… but without further details about “your” issue, nothing more we can suggest.
Yes, i eventually solved my problem, i was using Blynk.begin() with the wrong serial, i should have used The bluetooth serial, instead i was using the regular “Serial”