Does the pipeline settings JSON includes the "schema" field.

If you have full admin rights, you can update the existing pipeline settings to include the "schema" field.

Like 

curl -X PATCH https://<databricks-instance>/api/2.0/pipelines/<pipeline-id> \
-H "Authorization: Bearer <your-access-token>" \
-H "Content-Type: application/json" \
-d '{
  "schema": "your_default_schema"
}'

https://docs.databricks.com/en/delta-live-tables/properties.html

**schema **

Type: string

The name of the default schema for the pipeline, where all datasets and metadata for the pipeline are published by default. See Set the target catalog and schema.