Removing Sent Using Zoho Invoice from subject header on client emails

Removing Sent Using Zoho Invoice from subject header on client emails

I've tried locating where to turn off ZOHO branding in settings in various locations in ZOHO Invoice but to no avail. It is super tacky and unprofessional to have that at the end of every client email subject header. Any ideas on how to get rid of that?
Thanks
Jeremy