To be clear, this is the Victron Community which is not an official support channel (note the introductory paragraph of the Community Guidelines). Most of the people here are other system owners, enthusiasts, and some volunteer experts - this can be a very useful resource, but you can get wildly conflicting answers and opinions here too.
Your official support channel is the authorized Victron distributor/dealer from whom you purchased the unit.
That said, the above answer is correct - the MultiPlus is a DC device, do not run it without batteries connected.