Energy regulator Ofgem said it found ScottishPower did not have in place "appropriate management arrangements" to adequately train and monitor their doorstep and telesales agents, resulted in customers being given "misleading information".
"ScottishPower has accepted these failings, which have now all been rectified," Ofgem said.
The regulator continued: "The size of the payment reflects the impact of the sales practices on consumers and it also recognises ScottishPower’s cooperative engagement with Ofgem to put right their processes.
"Our investigation found no evidence of a strategy by ScottishPower to deliberately missell to customers."
More top news
A man, reportedly armed with a knife and a baseball bat, was detained close to the event and police cleared the area as a precaution.
A remarkably mild night
Thousands of people have gathered in the centre of Manchester for a vigil in the wake of the terror attack.