CRM and Invoice integration

CRM and Invoice integration

I used to have access to the invoice module in my CRM. Now, that option is gone. I tried to reintegrate, but the Invoice option is not present. 
If I log directly into Invoice and look at the integrated apps and the CRM is still present in my integrated apps, but I have this message next to the integrated CRM app. I have not changed editions, what has changed? How do I fix this?

Looks like there's a problem!

  • Your Zoho CRM edition does not support this module