The email address showing at the bottom of the invoice sent to clients can be changed by going to Partner Center > Administration > Customize > Under partner defaults tab; click on Email Settings > Sender Email > Change it and then apply the changes.
This is also the email address from which the platform will send reports, to which recipients can reply.
For Partners with multiple markets, repeat the same steps under the 'Markets' heading > click the pencil icon to select market and update email accordingly or simply apply the Partner branding configurations to the additional market(s).