WordPress has several solid was to add Head and Footer code to any website. One way is via Theme Options. Most solid themes have an option to add Head and Footer code by just pasting it in. But many themes don't have this option.

Two of ways to get around this are with plug-ins. One is called Head and Footer Scripts Inserter by Space X Chimp.

Another is called Insert Headers and Footers by WPBeginner.

Recently when a client of mine saw a blank screen while trying to add Google Adsense code into Head and Footer Scripts Inserter, we solved the problem by pivoting over to Insert Headers and Footers.