First, thanks for providing Duplicati and its documentation - great software!
Creating a new backup job, I set up the advanced option “–ssh-fingerprint” to verify server identity.
The fingerprint I copied from some place looked like “ssh-rsa 2048 55:32:0D:AF:99:7C:…”.
Duplicati failed, logging an error like “server fingerprint ssh-rsa 2048 55:32:0d:af:99:7c:… does not match”. However, the server’s fingerprint did match exactly with the value I entered in the configuration.
Being a bit confused, I realised the only difference was the case of the letters contained in the hex numbers.
I don’t know if there is a convention to only use lower case, but I did certainly not convert my fingerprint to upper case, and so I guess this case is not completely hypothetic.
Therefore, I suggest to improve the code doing the fingerprint check so it does not compare mere strings, but execute a comparison of the actual hex values.