我需要启用cors策略来到达我的API，我在我的nginx服务器文件上做了以下配置：

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    server_name api.domain.com;

    location / {

       proxy_set_header X-Real-IP $remote_addr;
       proxy_set_header Host $host;
       proxy_pass http://my_ip:6869/;

        set $ref "*";
        if ($http_referer ~* ^(http?\:\/\/)(.*?)\/(.*)$) {
          set $ref $1$2;
        }
        add_header 'Access-Control-Allow-Origin' $ref always;
        add_header 'Access-Control-Allow-Credentials' 'true' always;
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE' always;
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,signature,timestamp' always;
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range' always;

    }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/api.domain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/api.domain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

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但我一直得到以下错误：

Access to fetch at 'https://api.domain.com/data/key?matches=^art(.*)' from origin 'http://localhost:3500' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values '*, http://localhost:3500', but only one is allowed. Have the server send the header with a valid value, or, if an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

型
看起来add_header是在一个已经设置好的头文件之上添加的，但是我只有这个配置文件，看不到它可能来自哪里。
有没有办法弄清楚是什么设置了初始头cors策略，或者只是覆盖它而不是添加它？
先谢谢你了。