start server missing fullchain.pem about mediasoup-demo HOT 1 OPEN

[root@centos8 certs]# openssl genrsa -out privkey.pem 2048
Generating RSA private key, 2048 bit long modulus (2 primes)
..............................................................................................................+++++
...............+++++
e is 65537 (0x010001)
[root@centos8 certs]# openssl req -new -key privkey.pem -out csr.pem
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:
State or Province Name (full name) []:
Locality Name (eg, city) [Default City]:
Organization Name (eg, company) [Default Company Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (eg, your name or your server's hostname) []:
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
[root@centos8 certs]# 
[root@centos8 certs]# openssl x509 -req -days 365 -in csr.pem -signkey privkey.pem -out certificate.pem
Signature ok
subject=C = XX, L = Default City, O = Default Company Ltd
Getting Private key
[root@centos8 certs]# cat privkey.pem certificate.pem > fullchain.pem
[root@centos8 certs]# ls
certificate.pem  csr.pem  fullchain.pem  privkey.pem