The message you are trying to access is permanently deleted.
I notice in the US documentation there is an option to generate an email collection form that can be embedded into an existing website for email address collection/subscription however this does not seem to be available for the AU based Marketing.
Can this be offered also ? Presently the only way to do this is to follow a link to a very generic looking page.
AU:
Get Started with Customer Information Collection | Square Support Centre - AU (squareup.com)
US (see reference to embedded signup form):
Get Started with Customer Information Collection | Square Support Center - US (squareup.com)
Square Community