adding invoice spec
adding invoice spec

prburke/netsuite,charitywater/netsuite,mavenlink-solutions/netsuite,greggroth/netsuite,NetSweet/netsuite,centro/netsuite,nurelm/netsuite,oafridi/netsuite,sherriously/netsuite,littlebitselectronics/netsuite,jheth/netsuite,breestanwyck/netsuite,jeperkins4/netsuite,stripe/netsuite,dropstream/netsuite,PayloadDev/netsuite