If you have a plan and can't make full payment you need to change the plan with IRS, and fees are charged to do that. You can do it on line or on the phone (on line fees are lower)

Or, are you are talking about a deferred payment plan with Intuit rather than the IRS ?  Your post is not clear.

If that's the case, call customer support.  We are just (mostly)  fellow software users and can't assist with that.