Lead Source not syncing to SF

[Anonymous]

Hi - 
We have new leads filling out forms and I have a change data value step in the flow to change Lead Source if empty to Banner Ad. The Lead source is changing in Marketo but not in Salesforce - it is also throwing notification exceptions telling me it cannot update the lead source because there is already a value there..when I know there isn't! Please help! thank you

[Anonymous]

There might be a couple of issues.

1. Lead Source is field blocked (although this should not matter if the source=empty)
2. SFDC is also field blocking or the Marketo user is not allowed to update that field.