The difference is a guaranteed installment agreement vs the regular installment agreement. If you meet the requirements below, one of which is paying the full tax liability within 3 years, then the IRS HAS to approve your installment agreement request.
Guaranteed Installment Agreements
As an individual taxpayer, you have the right to an agreement without submitting a financial statement if:
- The amount of tax you owe (not counting interest and penalties) is less than $10,000
- You (and your spouse, if you filed joint) have filed and paid all taxes due for the previous five years
- Neither you (nor your spouse, if you filed joint) have had an installment agreement with the IRS in the previous five years
- You can pay the full amount within three years
- You agree to pay the liability before the period for collecting the tax expires
- You comply with the tax laws during agreement
If you don't meet these requirements, then you have to file for another type of installment agreement which can be up to 72 months, but the IRS does not have to approve your agreement and then can request more information from you, such as financial documents. If you owe less than $50,000, then it is possible to also file a streamlined agreement online directly with the IRS. If you owe more than $50,000, then you have to mail by mail using Form 9465.
https://taxpayeradvocate.irs.gov/get-help/installment-agreements#apply
https://www.irs.gov/individuals/online-payment-agreement-application
https://www.irs.gov/pub/irs-pdf/f9465.pdf
