Hi. I have a Synology box, and I understand how that particular update system works.
The reason it is asking you for those values, is because the way that the Synology package manager installs WordPress, it doesn’t give it the proper permissions to write to its own files locally. Thus, WordPress needs some other way to access the files in order to write to them.
If you install an FTP server, then you can give it the correct path and credentials for that, and thus allow WordPress to access the same box it is on via FTP, and it can then use that connection to write those files.
Alternatively, if you have SSH access to the synology box, then giving it that information will allow it to do much the same thing.
Basically, WordPress is trying to write local files. For security, it needs to write those files using the correct user account, which is the same as the user account as the files WordPress itself is running under.
None of the 1&1 or Let’s Encrypt is relevant here. What it is looking for is access to the box that the WordPress instance is actually running on. Local access. Even though you normally think of FTP or SSH as ways to access other servers, here, it’s looking for ways to access itself, but using the proper user credentials.
The easy way is to use the package manager to install an FTP server, then create an account on that system to allow access to the WordPress install files, and then give that FTP info to WordPress to perform those updates. A somewhat less easy way is to not use the Synology Package Manager to install WordPress at all, but to instead do-it-yourself so that you can give proper permissions to the system.
And finally, it is probably best to not use a Synology NAS device to run WordPress, or any other web server program, on the public internet. The Synology NAS devices are great for local usage and for file management, but they are not necessary intended to be always-on servers for public web sites. Consider using a real hosting service instead.
