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.
You can find digital copies of most IRS notices in your online account, under the 'Notices and Letters' section.