You didn't find the invoice because it was deleted, as it is incorrect.
Here are the steps taken, my expected outcome, and what actually is seen/generated:
1. Click on "add member". Expectations, create a new member, add a membership, and send an invoice with a payment link in the email.
a. clicked on add member, and then chose an existing wordpress user.
b. the next option is to choose a membership and check a checkbox for "create invoice"
c. the next option is to manage the start and enddate of the membership.
d. apparently I shouldn't press "create invoice" in the previous screen, because it sends a notice that the membership is active, paid, and started right away.
basically, the user is created, but the subscription becomes active immediately.
Also, now when an admin user views the invoice for the "managed subscription", it now also shows the other "active" membership.
So far, the new user is NOT able to access anything, and has NOT received anything concerning the modified, "managed" subscription.
I have attached several screenshots. At this point, I am not going to troubleshoot this further. if you wish login to a dev site, to troubleshoot these issues, I can provide it. However I must move on and use another solution, to get this site into production mode. If you can solve these multiple issues, you can message me, and perhaps on another site, I will use this product. For now though, I regard it as a non-working plugin, with huge bugs.