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Quick steps
Not every meter speaks IEC 62056-21. Look at the line first with Idle line and Autobaud 5 s. A sign-on that is not ACKed makes an IEC meter stream its whole readout at 300 baud, which keeps its line busy for minutes. Never send password (P1) or write (W1) commands to a meter in service.
Command
Connect, then try Info.