I have a multi-select field that has options: Yes, No, Confirmed.

The field is set to ["Yes"], and I want to be set to ["Yes", "Confirmed"]

I found that I can't just add one - I have to clear it first. So instead of:

contact["Next delivery"].push("Confirmed")
contact.save

I have to do:

result = contact["Next delivery"].push("Confirmed")
contact["Next delivery"] = []
contact["Next delivery"] = result
contact.save