There is a difference between Client ID and Client Matter ID, because Invoice Submitter was putting the Client Matter ID in the Client ID field. The Client ID is an internal ID your firm/company associates with your client ABC. It can be alpha, numeric, or an alpha/numeric value. For example it could be 1234, ABC, 99LFirm, 100LF, etc. However if referring to the Client Matter ID, then that is provided by the client. These are the matter’s that your firm/company are doing work on.