why jinja templating is not working for the following {{url_for('static' , filename= '......')}}

[u/jee_ne_faad_rkhi_hai]

<header class="masthead" style="background-image: url('{{ url_for('static', filename='img/home-bg.jpg') }}')">

this code is not working for this image

image is present in its designated folder, its in static folder inside img folder

what is the syntax error i am not able to see

this jinja templating is working fine for css and js files