You can pre-determine a Form 1099's filing status by passing a test value in the formFields.accountNumber request attribute.
Passing 111 as the accountNumber during a Form 1099 creation will mimic an form filing response of ACCEPTED once the filing action is taken. This status means both the IRS and applicable state tax authorities have acknowledged and accepted this information return.
Passing 222 as the accountNumber during a Form 1099 creation will mimic an form filing response of REJECTEDonce the filing action is taken. This status means either the IRS or applicable state tax authorities have deemed this form unacceptable and can not proceed with the filing.
Other ways to receive a filing rejection
Form 1099s will also be placed in a REJECTED status automatically if either the Payee or Payer have an associated MISMATCH Tin Verification.
To mimic this behavior in sandbox, simply pass in a test tin value that corresponds to a MISMATCH when creating a Form 1099.