Hi Jeshurun77,
I believe the forum post you linked in your first post is slightly misleading for what you are attempting to do. First off, please understand that Method Reports are built using different technology then QuickBooks reports, so they are not interchangeable. This means, if you have predefined Invoice Reports in QuickBooks for example, you will never be able to view this Invoice Template from Method, it only exists in QuickBooks. The same would be if you created an Invoice Template in Method, you can only access this template from Method, it does not exist nor can it be synced with QuickBooks.
You still have a couple of options depending on what would work best for you. One option is, if you prefer to do your invoicing from QuickBooks, there is an option at the bottom of most Method Transaction screen with a checkbox labelled "To be printed in QuickBooks?" When this option is selected, and you save the transaction from Method, the transaction will get synced to QuickBooks, and from QuickBooks, if you then go to File->Print Forms, then select your transaction, in this case "Invoices". Here, you should see a list of all your Invoices sent from Method to be printed from QuickBooks, from here, you can then select to print these off. These instructions are only valid for QuickBooks Desktop accounts as far as I know.
Your second option would be to use the default Invoice Template in Method, you can print this or email it to your Customer. If you require to have a customized version of this Method Invoice (like to mimic the one in QuickBooks), you do have the ability to customize the existing Invoice yourself to cater to your requirements. If this option is of interest to you, you can take a look at this Help Center Article, we provide a few videos that should help you understand how to use the Report Designer for Method, there is also a download link at the top of the page.
-Ben