ISPConfig fresh installation on Debian 10, but acme.sh failed to issue certificate

We follow this tutorial, https://www.howtoforge.com/perfect-server-debian-10-nginx-bind-dovecot-ispconfig-3.1/ except we skipped installing Jailkit, Mailman, and Roundcube. When we did ISPConfig installation, we got the following messages:

req: Can't open "smtpd.key" for writing, No such file or directory
PHP Warning: symlink(): No such file or directory in /tmp/ispconfig3_install/install/lib/installer_base.lib.php on line 2827​

and when we answered "y" on SSL question, we got these messages:

Checking / creating certificate for our.hostname
Using certificate path /root/.acme.sh/our.hostname
Using nginx for certificate validation
acme.sh is installed, overriding certificate path to use /root/.acme.sh/our.hostname
[Wed 25 Aug 2021 05:33:49 AM WIB] Please add '--debug' or '--log' to check more details.
[Wed 25 Aug 2021 05:33:49 AM WIB] See: https://github.com/acmesh-official/acme.sh/wiki/How-to-debug-acme.sh
Issuing certificate via acme.sh failed. Please check that your hostname can be verified by letsencrypt
Could not issue letsencrypt certificate, falling back to self-signed.​

We have checked the our.hostname with https://tools.letsdebug.net/, everything is okay. Note:

1. In the explanation above, we replaced our real domain with "our.hostname"
2. This is 2nd installation, after the 1st one failed. We deleted /usr/local/ispconfig & dbispconfig database in MySQL, before 2nd installation.

 

I went through the same issue, spent days and days trying different ways. Till, Norell and others helped and contributed to my same issue.
Install isp, follow the setup tutorial to the letter, then on panle, web01 (where in tutorial it states to press enter) these are the servers you will need to

Code:

ispconfig_update.sh --force
choose nightly

as till suggests, you may also need to delete the self signed cert which is in

Code:

//usr/local/ispconfig/interface/ssl/

and delete all ispconfig.* files.
then retry