I am placing in an amount for the irs monthly payment but it’s getting rejected

If you choose not to answer, select too low of an amount, or let the IRS pick a payment amount for you; your minimum payment will be the amount that you owe divided by 72.

https://turbotax.intuit.com/tax-tips/tax-payments/what-is-the-minimum-monthly-payment-for-an-irs-ins...

Do NOT complete the installment payment forms in the TT program ... instead choose to mail in a check for the balance due then  fill out the installment forms on the IRS website directly where the fee is less ... www.irs.gov/payments.