Invoice_Text modification

I need to modify the invoice that a subscribed user is emailed after payment. I see where the email template is controlled and the email template has the following:

Thank you for your order. You may find order details below:
%invoice_text%​

I need to control the %invoice_text%, but can't seem to find where it is generated in amember. Can someone point me to the correct location?

Is %invoice_text% plain text only? Is there a HTML version of %invoice_text% or do we need to use

Code:

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Thanks