We're trying to pass some account ID GUIDs from Marketo to Dynamics, but our testing has failed, is it possible to send GUIDs in a Microsoft Custom Field on the lead record when the originating field type in CRM is a Lookup field?
You should be able to sync any field from MSD to Marketo so long as you're able to select it from the field sync list.
However, I'm going to assume here that your sync is already up and running. If so, please read the documentation to gain a better understanding of what you need to do and what Marketo can do to help: Microsoft Dynamics Sync: Field Sync - Marketo Docs - Product Docs
Yes, we're already synced and we haven't had any problems creating new fields and sending content in those fields for the most part, its just this one lookup field we're having issue with the data coming back into CRM.
Ahh I think I get you now. So, in MSD, you have a lookup type field. However, you want to update this lookup type field not via the lookup, but via Marketo sync? Logically, this won't work. You're going to want to focus on changing the value in the field that it's looking up IF that field is also in Marketo.