Hi, team.
Long story short:
I was hosting my application in Amazon Web Services in a LEMP Instance. I then decided to move to Digital Ocean because their instances are not allowed to send emails.
My app, in the AWS instance, was able to upload photos, write to the database, and communicate with an external API.
In Digital Ocean, however, I’m not able to upload photos. In /var/log/nginx/error.log this is the output:

2020/05/18 03:28:17 [error] 10851#0: *174 FastCGI sent in stderr: "PHP message: PHP Notice:  A non well formed numeric value encountered in /usr/share/nginx/html/admin/core/controller/class.upload.php on line 2667 PHP message: PHP Notice:  A non well formed numeric value encountered in /usr/share/nginx/html/admin/core/controller/class.upload.php on line 2667" while reading response header from upstream, client: 181.115.109.228, server: _, request: "POST /admin/index.php?action=addproduct HTTP/1.1", upstream: "fastcgi://unix:/run/php-fpm/www.sock:", host: "165.227.91.80", referrer: "http://165.227.91.80/admin/index.php?view=newproduct"

You’d believe that there’s an error in class.upload.php on the line 2667, however, this is not the case. As I’m telling you, everything works as intended in AWS. /var/log/php-fpm/error.log does not show any error. This is the output:

[18-May-2020 01:39:40] NOTICE: fpm is running, pid 10826
[18-May-2020 01:39:40] NOTICE: ready to handle connections
[18-May-2020 01:39:40] NOTICE: systemd monitor interval set to 10000ms

The upload directory is /usr/share/nginx/html/admin/storage and the permissions are set to 777.
Please, help.