Hi,
With the PDF invoice plugin, there can be some issue when you add a logo to the invoice as the HTML2PDF library used to generate the PDF can have trouble retrieving the image.
But in your case, you're not using that plugin (as far as I can see there is no purchase of that plugin from your user account).
So in that case, you just have to edit the view file displaying the invoice (in the backend it's the file "invoice" of the view "order") via the menu Display>Views and add the HTML tag of your image in the code where you want the logo.
So for example, you can start adding such code at the beginning:
where XXX is the URL of your logo that you previously uploaded via the Joomla media manager or FTP.