Custom Taxonomies Not Working – Radio or Single Text field

Latest software on all –

Need to connect custom taxonomy, but having difficulty.

Can connect with Radio, but can’t choose a default term (which I need to be able to submit as a hidden field) – upon saving form, the default selection is no longer selected.

Try the single line, but under Advanced, when I click “save to taxonomy” – no taxonomies are listed. I can add the default term, but it doesn’t connect with taxonomy, so on submission, there is no term assigned.

Regardless of which method I choose, I can’t connect the taxonomy and choose a default term to submit as a hidden field.