Set terms in a custom post

I know this is an old question, but the tax_input array should probably look like this since it appears to be hierarchical like a category:

'tax_input' => array('artist-category' => array( 3 ) //use the ID of the category, not the name of the category

From WordPress Codex on wp_set_post_terms

If you want to enter terms of a hierarchical taxonomy like categories,
then use IDs. If you want to add non-hierarchical terms like tags,
then use names.

Resources:

• https://developer.wordpress.org/reference/functions/wp_insert_post/#notes
• https://codex.wordpress.org/Function_Reference/wp_set_post_terms#Parameters