Signing up for Zoho Invoice - email

Signing up for Zoho Invoice - email

I am a zoho mail user and I want to sign up for Zoho Invoice. When I attempt to sign up using my zoho email xxx@zyzcompany.com

I see this message: Email address already exist.......

Yes it exists, because I set it up using Zoho...it is my company email and I want to use it in Zoho Invoice...

I was thinking of a paid account but if Zoho can't fix this then I will go to competitive product...