Where is fallbackToDefaultTenant set?

I am using the flowable default rest-postgres docker image. I want to be able to use the fallback to default tenant ID when starting process instances, but it is not working.

I am looking at the file StartProcessInstanceCmd.java and I see this line:

if (fallbackToDefaultTenant || processEngineConfiguration.isFallbackToDefaultTenant()) {

Based on the error message I am receiving:

  "message": "Bad request",
  "exception": "Process definition with key 'testProcess' and tenantId 'cpy5' was not found"

it is not going into that conditional. So, fallbackToDefaultTenant is definitely false. Where would I set this? Some environment variable in the Docker container?