In my case I've wanted to change the SSL certificate, because I've e changed my server so I had to create a new CSR with this command:
openssl req -new -newkey rsa:2048 -nodes -keyout mysite.key -out mysite.csr
I have sent mysite.csr file to the company SSL provider and after I received the the certificate crt and then I've restarted nginx , and I have got this error
(SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)
After a lot of investigation, the error was that module from key file was not the same with the one from crt file
So, in order to make it work, I have created a new csr file but I have to change the name of the file with this command
openssl req -new -newkey rsa:2048 -nodes -keyout mysite_new.key -out mysite_new.csr
Then I had received a new crt file from the company provider, restart nginx and it worked.