Letsencrypt integration with HAProxy and acme.sh - quirks

While following these instructions I’m stumbling across the following:

acme@mail:/root$ whoami
acme@mail:/root$ acme.sh --register-account
touch: cannot touch '/var/lib/acme/.acme.sh/http.header': No such file or directory
[Fri Nov 10 11:17:48 AM CET 2023] Create account key ok.
[Fri Nov 10 11:17:49 AM CET 2023] No EAB credentials found for ZeroSSL, let's get one
[Fri Nov 10 11:17:49 AM CET 2023] acme.sh is using ZeroSSL as default CA now.
[Fri Nov 10 11:17:49 AM CET 2023] Please update your account with an email address first.
[Fri Nov 10 11:17:49 AM CET 2023] acme.sh --register-account -m my@example.com
[Fri Nov 10 11:17:49 AM CET 2023] See: https://github.com/acmesh-official/acme.sh/wiki/ZeroSSL.com-CA

What does it mean and is there something wrong with that?
And could someone explain, what this registration is good for? And what the purpose behind is?

I got further meanwhile.
Went through the Wiki. Was able to obtain the certificates.
I thought let acme.sh fetch the certificates for more than just the www.mydomain,org domainname.
But it looks as though haproxy doesn’t like a bundled certificate. (multidomain cert).

Will try the Wiki again. The step:

root@mail:~# echo "show ssl cert /etc/haproxy/certs/www.mydomain.org.pem" | socat /var/run/haproxy/admin.sock -
Can't display the certificate: Not found or the certificate is a bundle!

give this.

I solved it:

seems like the acme.sh --issue challenge uses an ECC (ec256) cert by default.
And HAPROXY doesn’t seem to accept this.

Changing the issue command by specifying the --keylength,made it work:

 acme.sh --issue -d mydomain.org --stateless --keylength 2048

I had some other quirks. The ec-256 certificate was not the problem.
Cannot reproduce the problem anymore.