Hi Vicky, we had a similar error where we were trying to merge fields that were datetime into a Marketo date field (mismatch from SFDC). We had to change the type of the field in Marketo, but in order to even know what field was causing the issue we had to contact support. Unfortunately, the error messages that they provide can be very cryptic and not really give you the information that you need to make updates/decisions.
I'd reach out to support.
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