How make htaccess for single-page app within a sub-path in URL?

Just adding answer for reference.

The commnet from @Croises:

"The same (with [QSA] not [QA]) but in the webapp directory"

Worked for me.

The ".htaccess" must be on the subdieretory.

Example working ".htaccess":

<ifModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule (.*) index.html [QSA,L]
</ifModule>

The only diference is "[QA,L]" to "[QSA,L]"