Late reply. Same Problem. I edit /usr/local/emhttp/plugins/tasmotapm/status.php and add the number of channel to the array, looks like this:
$json = array(
'Total' => $data['StatusSNS']['ENERGY']['Total']['0'],
'Today' => $data['StatusSNS']['ENERGY']['Today']['0'],
'Yesterday' => $data['StatusSNS']['ENERGY']['Yesterday']['0'],
'Voltage' => $data['StatusSNS']['ENERGY']['Voltage'],
'Current' => $data['StatusSNS']['ENERGY']['Current']['0'],
'ApparentPower' => $data['StatusSNS']['ENERGY']['ApparentPower']['0'],
'ReactivePower' => $data['StatusSNS']['ENERGY']['ReactivePower']['0'],
'Factor' => $data['StatusSNS']['ENERGY']['Factor']['0'],
'Power' => $data['StatusSNS']['ENERGY']['Power']['0'],
'Costs_Price' => $tasmotapm_costs_price,
'Costs_Unit' => $tasmotapm_costs_unit
);
On http://IP_OF_YOUR_DEVICE/cm?cmnd=Status%208 you seen the number of the channel you need.