Ubuntu 20.04 when I tried to install RabbitMQ it showing this error

I followed this website to install RabbitMQ https://attacomsian.com/blog/install-rabbitmq-macos-ubuntu

On the 5th step where it install RabbitMq, When I run the command I get this error

rabbitmq-server.service - RabbitMQ Messaging Server
     Loaded: loaded (/lib/systemd/system/rabbitmq-server.service; enabled; vendor preset: enabled)
     Active: activating (auto-restart) (Result: exit-code) since Fri 2021-08-20 10:11:27 IST; 5ms ago
    Process: 361473 ExecStart=/usr/sbin/rabbitmq-server (code=exited, status=1/FAILURE)
   Main PID: 361473 (code=exited, status=1/FAILURE)
dpkg: error processing package rabbitmq-server (--configure):
 installed rabbitmq-server package post-installation script subprocess returned error exit status 1
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for systemd (245.4-4ubuntu3.11) ...
Errors were encountered while processing:
 rabbitmq-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

when I run sudo apt update, this error is showing

    E: The repository 'http://www.rabbitmq.com/debian testing Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Please follow the official documentation: https://www.rabbitmq.com/install-debian.html#apt-quick-start-packagecloud

with a simple script, you can easily install rabbitmq on ubuntu.

for example:

#!/usr/bin/sh

sudo apt-get install curl gnupg apt-transport-https -y

## Team RabbitMQ's main signing key
curl -1sLf "https://keys.openpgp.org/vks/v1/by-fingerprint/0A9AF2115F4687BD29803A206B73A36E6026DFCA" | sudo gpg --dearmor > /usr/share/keyrings/com.rabbitmq.team.gpg
## Launchpad PPA that provides modern Erlang releases
curl -1sLf "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0xf77f1eda57ebb1cc" | sudo gpg --dearmor > /usr/share/keyrings/net.launchpad.ppa.rabbitmq.erlang.gpg
## PackageCloud RabbitMQ repository
curl -1sLf "https://packagecloud.io/rabbitmq/rabbitmq-server/gpgkey" | sudo gpg --dearmor > /usr/share/keyrings/io.packagecloud.rabbitmq.gpg

## Add apt repositories maintained by Team RabbitMQ
sudo tee /etc/apt/sources.list.d/rabbitmq.list <<EOF
## Provides modern Erlang/OTP releases
##
## "focal" as distribution name should work for any reasonably recent Ubuntu or Debian release.
## See the release to distribution mapping table in RabbitMQ doc guides to learn more.
deb [signed-by=/usr/share/keyrings/net.launchpad.ppa.rabbitmq.erlang.gpg] http://ppa.launchpad.net/rabbitmq/rabbitmq-erlang/ubuntu focal main
deb-src [signed-by=/usr/share/keyrings/net.launchpad.ppa.rabbitmq.erlang.gpg] http://ppa.launchpad.net/rabbitmq/rabbitmq-erlang/ubuntu focal main

## Provides RabbitMQ
##
## "focal" as distribution name should work for any reasonably recent Ubuntu or Debian release.
## See the release to distribution mapping table in RabbitMQ doc guides to learn more.
deb [signed-by=/usr/share/keyrings/io.packagecloud.rabbitmq.gpg] https://packagecloud.io/rabbitmq/rabbitmq-server/ubuntu/ focal main
deb-src [signed-by=/usr/share/keyrings/io.packagecloud.rabbitmq.gpg] https://packagecloud.io/rabbitmq/rabbitmq-server/ubuntu/ focal main
EOF

## Update package indices
sudo apt-get update -y

## Install Erlang packages
sudo apt-get install -y erlang-base \
                        erlang-asn1 erlang-crypto erlang-eldap erlang-ftp erlang-inets \
                        erlang-mnesia erlang-os-mon erlang-parsetools erlang-public-key \
                        erlang-runtime-tools erlang-snmp erlang-ssl \
                        erlang-syntax-tools erlang-tftp erlang-tools erlang-xmerl

## Install rabbitmq-server and its dependencies
sudo apt-get install rabbitmq-server -y --fix-missing

and ..

root@ubuntu-focal:/home/vagrant# rabbitmqctl status
Status of node rabbit@ubuntu-focal ...
Runtime

OS PID: 4038
OS: Linux
Uptime (seconds): 14
Is under maintenance?: false
RabbitMQ version: 3.9.4
Node name