Free text invoice inbound AIF

I am trying to setup an inbound AIF port for free text invoices. When testing a bare bones XML on the port, I get the following error on the line level: “The main account does not exist”. The only enabled field on the line level is DefaultDimension. I have tried including the following in the XML but get the same error:">]( MainAccount 1010

Any thoughts on what may be causing the error?