@hubspot - we are trying to begin using Hubspot for all contracting but when I found this flaw it stopped us. We need to be able to add credit memos and until the negative numbers are allowed this is a show-stopper. If there are any workarounds please let us know because we are going to have to look at alternative products now and stop the growth with Hubspot as this was something I was very clear we would be doing and could do with Salesforce.