You might want to update webapp manifest link to:
<link rel="manifest" href="./manifest.json" crossorigin="use-credentials"/>
This is because browsers make requests for web app manifests without credentials, even if the file is on the same domain as the page.
And if page is behind some sort of WAF which gives you cookie, this cookie is not sent when manifest query is made and therefore you are unable to install webapp in this case.
You might want to update webapp manifest link to:
<link rel="manifest" href="./manifest.json" crossorigin="use-credentials"/>This is because browsers make requests for web app manifests without credentials, even if the file is on the same domain as the page.
And if page is behind some sort of WAF which gives you cookie, this cookie is not sent when manifest query is made and therefore you are unable to install webapp in this case.