If you currently have an approved installment agreement with IRS and are currently making installment payments to IRS, then you may stop making those installment agreement payments when you submit a Periodic Payment offer. This will allow you to make your payments required under the Periodic Payment guidelines. You do not have to make both installment agreement payments and periodic payments at the same time.
Similarly, if you currently have an approved installment agreement with IRS and are currently making installment payments to IRS, then you may stop making those installment agreement payments when you submit a Lump Sum Cash offer. If you submit a Lump Sum Cash offer, you must submit an initial payment of 20% of the total offer amount with your application. During the review process, no other payments are required, until you receive the written acceptance of the offer, then you must pay the remaining balance of the offer in five or fewer payments.