I’m not an Integromat expert, but I suspect the issue is that single-select and multi-selects are actually types themselves, under the hood.
So it is possible to use Integromat to assign a value for a single-/multi-select field, but that value needs to already exist (as an entity of the single-/multi-select type).
I am not aware that you can use Integromat to create new entities of the (hidden) single-/multi-select types, so I think you have to either:
- manually create in Fibery all the tags that might be needed
- define a standard Fibery type for tags (not a single-/multi-select) and then create the tags in Integromat as needed, prior to creating the subscribers and updating them to link to the tags.