How to find more information about error 1000 during sending email from form?

To send email from our system via Eloqua we use REST API call /api/rest/2.0/data/form/{id}/batch

https://docs.oracle.com/en/cloud/saas/marketing/eloqua-rest-api/op-api-rest-2.0-data-form-id-batch-post.html

We call a form, and on the form, we use Send Submitter process to send e-mails.

In our DEV environment we don’t have any issues.

In our UAT environment sending email intermittently fails with error:

        "processingStepErrors":[

           {

              "type":"ProcessingStepError",

              "errorCode":1000,

              "errorDescription":"Please contact administrator",

              "errorMessage":"ProcessingStep : ProcessingStepGenericError",

              "processingStepDisplayName":"Send Email",

              "processingStepId":"237",

              "processingStepTypeId":"5"

           }

It can fail a few times in a row and after that start working again for exactly the same parameters (