2co Payment Installation Error

Hello I just purchased 2CO but having installation error. Below is the error during installation:

"Your Extension appears to be written for an older version of Joomla!. You must enable the System - Legacy Plugin in the Plugin Manager if you wish to complete this task."


AND AFTER ENABLING THE System - Legacy in the Plugin Manager:

"Plugin Install: No plugin file specified"

Thanks

Hello Ola,
Did you go to EShop->Plugins->Payments to install the 2CO payment plugin from there?
Sincerely, Giang