We have been trying for weeks to send our opportunity data up to Marketo from our own CRM. Finding documentation on the syncMObjects API call for the type Opportunity has been problematic. When making the call we get back the error that "Input string was not in a correct format" and yet nothing we try seems to resolve the problem. It would help to have a list of all of the attributes and what value types it expected or allowed.
Adchoices