I’m not sure what your field type is. So depending of the field type, we have different solution.
taxonomy field, as the plugin doesn’t store value in post meta, there’s no need to submit value via
meta_box field. Instead, after creating tags, you should send another request to set post terms, e.g. set the created tags as a term for the post.
taxonomy_advanced field, the value saved in the DB is the
term IDs (separated by commas), not term slugs. So I think you still need to send 2 requests: one for creating tags and gets their IDs, one for adding those IDs to post meta via
I hope that makes sense.