Saving Values from Gravity Form MultiSelect

I’m using Gravity Forms to register users. One field is a multiselect of a custom taxonomy.

I’m passing those values to the Bxcft_Field_Type_MultiSelectCustomTaxonomy, but it’s not saving them. I’ve tried saving the taxonomies’ ID, slug and name, none of which works.

Is there a way to pass these values so that the multiselect stores them?