help with adding custom headers

help with adding custom headers
 this is a screenshot from an example.
My code doesn't work either.
in Mainifest.xml
``
in string.xml
`[{ \"include\": \"https://qwerty.com/.well-known/assetlinks.json\" }] `

file from site: https://qwerty.com/.well-known/assetlinks.json
`[{
"relation": ["delegate_permission/common.use_as_origin"],
"target" : { "namespace": "android_app", "package_name": "my.app.android",
"sha256_cert_fingerprints": ["52:52:52:52:36:D9:4E:F3:DB:E5:3E:0E:7A:2D:3C:D8:08:8E:7A:FF:56:FC:30:E0:59:AC:05:43:CE:CE:CE:CE"] }
}]`
the rest of the code is as in the example [(https://developer.chrome.com/docs/android/custom-tabs/headers/)]