If you open the project view for your HREFLang Builder account and it is full of red rows it is due to the tool not being able to detect the country or language for that source file.
For example, if your site uses the format of www.mysite.com/ar/page.html and you use the syntax of language then the tool would assume this is an Arabic site but does not know for which country.
If you had set this as a country in which case/ar was for Argentina, we do not know if the site is in Spanish or English. So you would need to tell is which it is.
To set the country or language simply click the Edit File button to bring up the entry for this source file. Click the Country Language selector and scroll to find the appropriate combination of country and language or you can choose a Global Language. For example, if the source file is for your French language site you should select “Global French” this is will create the HREFLang entry <link rel=”alternate” hreflang=”fr” href=”https://www.example.com/fr/” />
If the site is a language version for a specific country you select that combination. For example, if the source file represents your Spanish URL’s for Argentina, click the Country Language selector and scroll or type “Argentina” to find “Argentina” if the site is for Argentina but in English choose Argentina English this is will create the HREFLang entry <link rel=”alternate” hreflang=”en-AR” href=”https://www.example.com/ar/” />