Does anyone have experience with installing 3rd party javacript?

I have a script from a 3rd party vendor that when try to I install in Content/Configuration/HTML Head/Scripts and Style Sheets returns a 404 error.

I have also tried pasting the script directly before the </body> tag in app/design/frontend/Smartwave/porto/Magento_Theme/layout/default.xml with no success (the script is there, but doesn’t work or appear on the frontend when I inspect the code).

Can anyone point me to some basic how-to resources for doing this? Thank you!