The American Express functionality will be available from version 1.10.0 of the PayPlug module.
To benefit from this, you can contact your account manager or our Support service via this link
For activation, simply go to your Woocomerce back office and activate the feature as shown below in the menu > Plugins >Installed plugins > Payplus > Settings > Amex Payments > Switch to ON > Update Settings
To find out more about American express's feature, you can read our dedicated FAQ