Installment agreements are not usually the best solution for a tax Problem. But some people want them anyway. If you all more than $25,000 the IRS will want you to fill out the form 433.
If the IRS determines the information is accurate they will review your expenses and allow those which they deemed to be necessary. They will then seek the maximum amount you can pay.

There are times when the service will refuse an IA

1. When your expenses are deemed to be beyond the IRS ‘allowable’ amount.
For example credit card payments are not “allowable’

2. If the IRS decides the information you provided is Not accurate or truthful (The IRS will sometimes check public records to see if you own property… They will then check to see if you identified that property on your form)

3. You had an earlier installment agreement and defaulted on it. This one’s a little gray. I have seen the Service go both ways on this.

Keep in mind that as a general rule installment agreements should be your very last choice.