How to fix OpenSSL signed file signature verification error?

Question

PHP

There is a service where you need to send an xml file, after signing it with a key.
ran the command:

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout privateKey.key -out certificate.crt

2 files appeared in the user's root folder (root):
certificate.crt and privateKey.key I transferred privateKey.key
to the project folder, or rather, I had to send it to the service in /simplesamlphp/cert/certificate.crt so that it could verify the received data against it. Generally sent. I sign the xml file using simplesamlphp. There are no errors, everything has been checked, deduced, everything is signed. The service returns an error: 350Unable to validate Signature Could this be because I moved the privateKey.key file from my home folder to the project folder? And if not, what else could be the problem?