I can't enter my last name. it's more than 20 characters in length. But the 'last name' input box only allow to enter 20 characters.

[SherekaB]

Type as much of your name that you can fit and you will fine. The IRS only matches the first 5 characters of your last name to your social.

[hthierry84]

The turbo tax 2019 will not allow me to enter any of my last name in the last name box

!!!!!!!!

[JohnW222]

Just remove the final characters of your last name until it fits the acceptable format. 

It's alright if not all of the characters in your last name aren't included, since the IRS only uses the first few characters of the last name to match up with your SSN, verifying your identity.