Hi @cknoell - both errors looks like permission issues, where the user used to import dashboards into Kibana does not have the required Kibana privileges (esp. kibana_user). Can you double check that?
The second error has a 400 Bad Request return code, but I suspect that's a bug and it should be 403 Forbidden. This has been previously encountered by people importing dashboards from Beats at Failed to import dashboard 7.2.0 and I've opened a bug report at https://github.com/elastic/kibana/issues/40714.