You can verify your domain's ownership by adding a meta tag to your website's source code 👇
Within Hostinger Website Builder, access the website's integrations settings, find the Custom code field, and insert the given verification code there:
Save the changes and update your website. Then, verify your domain on Facebook's end.
In the Custom code field, you can paste as many codes as you need, simply paste one below another, and don't paste a code in the middle of another code.
P.S. If you choose DNS verification method, simply create a TXT record this way: How to Manage TXT Records in hPanel.