conf

gzip  on;
gzip_vary  on;
gzip_min_length  100;
gzip_buffers  16 8k;
gzip_proxied  any;
gzip_types
    text/plain
    text/css
    text/javascript
    application/json
    application/javascript;

Make Sure Gzip module installed with nginx

2>&1 nginx -V | tr -- - '\n' | grep _module | grep gzip

Output Should be : http_gzip_static_module

Configuration

Host Configuration file under server block.

gzip on;
gzip_disable "msie6";

gzip_comp_level 6;
gzip_min_length 1100;
gzip_buffers 16 8k;
gzip_proxied any;
gzip_types
    text/plain
    text/css
    text/js
    text/xml
    text/javascript
    application/javascript
    application/x-javascript
    application/json
    application/xml
    application/rss+xml
    image/svg+xml/javascript;

service nginx reload

Testing

curl -H "Accept-Encoding: gzip" -I https://example.com/

Have you tried to add 'gzip_comp_level level;'? It looks like you missed something in your configuration. Here you have a working example:

gzip on;
gzip_comp_level 2;
gzip_http_version 1.0;
gzip_proxied any;
gzip_min_length 1100;
gzip_buffers 16 8k;
gzip_types text/plain text/html text/css application/javascript application/x-javascript text/xml application/xml application/xml+rss text/javascript;
gzip_disable "MSIE [1-6].(?!.*SV1)";
gzip_vary on;