Upload Google Adsense code to PHP website.

Create an ads.txt file for 1 site
To prevent severe impact on revenue, download an ads.txt file then upload the file to the root level domain of each site:


It may take a few days for changes to update. If you’re using another ad network, remember to add the network to the ads.txt file. See the ads.txt guide for more details.


More information:

Create an ads.txt file for your site
Sign in to your AdSense account.
In the alert on your homepage, click Fix now.
Click the Down arrow Down arrow to open the "Create an ads.txt file for..." message.
Click Download. Your ads.txt file is automatically downloaded.
Upload the file to the root level domain of your site (for example, https://example.com/ads.txt).
Root levels are one level down from what’s listed in the public suffix list. For example, "google.co.uk" is a root domain of "co.uk" but "maps.google.co.uk" is not. See the IAB ads.txt specification.

Note: If you’re using another ad network, remember to add that network to your ads.txt file. Contact your ad network for their ads.txt information.