Income Accounts

Income Accounts

I'm new to Zoho Books and need a little help setting up income accounts.  How do I specify the income account to which revenue posts (when receiving invoice payment)?  Right now everything posts to "Sales" (except one random invoice, which for no apparent reason, posted to "Unearned Income"???).

I would like to track the different segments of service we provide by using separate income accounts.  We provide primary field services along with secondary support services.   Currently, I create a project with tasks, log time, generate an invoice from the project, then receive payment. I don't see anywhere along the way to specify the Income Account. 

I would like to be able to specify "Primary Services Income" and "Support Services Income" - preferably at the Task level. Is this possible?  If not, any alternative suggestions?

Any help is greatly appreciated.