I'm trying to enter my foreign income with a form 673 and the app is not taking it.

Foreign earned income is not reported using Form 673, Statement for Claiming Exemption from Withholding on Foreign Earned Income Eligible for the Exclusion(s) Provided by Section 911

It is reported using Form 2555, Foreign Earned Income

To enter Foreign Earned Income -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Less Common Income
On Foreign Earned Income and Exclusion, click on the start or update button

Or enter foreign income in the Search box located in the upper right of the program screen. Click on Jump to foreign income