Form 9465 can be included electronically with an e-filed return or paper-filed. When filing a paper return, complete Form 9465, attach it to the front of your client's return before mailing. They should receive a response to the request for installment payments within 30 days.
If you don't qualify for an IA through OPA, you may also request an IA by submitting Form 9465, Installment Agreement Request, with the IRS. When you request an IA using the form, generally, you'll receive a response from the IRS within 30 days notifying you of whether the IA request was approved or rejected.