Content Security Policy error

When I am trying to connect my desktop client - I get to Access Page. When I click Grant Access - nothing happens and I get the following error in the console:

Content Security Policy: The page’s settings blocked the loading of a resource at http://[domain]/login/v2/grant (“form-action”).

I have set up docker using docker-compose.yml and proxy via nginx.
My docker-compose is the same as here in the Base version - apache section.

Here is my nginx config:

upstream nextcloud {
    keepalive 64;

server {
    server_name [domain];

    location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Forwarded-Host $host;
        proxy_set_header X-Forwarded-Server $host;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";

        proxy_pass http://nextcloud;
        proxy_read_timeout 240s;

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/[domain]/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/[domain]/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

server {
    if ($host = [domain]) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    server_name [domain];
    return 404; # managed by Certbot