How to install letsencrypt on debian 8?

Question

Debian

I do as it is said at the office. site
To do this, I had to add jessie-backports as stated here
But letsencrypt is not installed due to "unmet dependencies":

$ sudo apt-get install -t jessie-backports letsencrypt
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 letsencrypt : Depends: python-letsencrypt (= 0.5.0-1~bpo8+1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Trying to install dependencies:

# apt-get install -t jessie-backports python-letsencrypt
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 python-letsencrypt : Depends: python-acme (>= 0.5.0) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

# apt-get install -t jessie-backports python-acme
Reading package lists... Done
Building dependency tree
Reading state information... Done
python-acme is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 31 not upgraded.

apt list dependencies shows:

# apt list python-letsencrypt
Listing... Done
python-letsencrypt/jessie-backports 0.5.0-1~bpo8+1 all

# apt list python-acme
Listing... Done
python-acme/jessie-backports,now 0.6.0-1~bpo8+1 all [installed]

How to install it correctly?

Answer 1

https://debian.pro/1925
https://debian.pro/2152
Install packages with a specific version, it will be clearer what is happening.
apt-get install package=version -t repo
Well, in general, most likely, some kind of meat from the repositories in the sources.list. Some testing is connected, for example.