How to log into crash using ssh key?

Question

Java

There is such a thing www.crashub.org , which is integrated into Spring Boot. Allows ssh (and other protocols) to communicate with the application.
I'm not strong in everything related to ssh and keys, so I've already broken my head on how to implement key pair authorization.
The documentation says: just add two lines to the config: www.crashub.org/1.3/reference.html#_key_authentication
shell.auth=key
shell.auth.key.path=/home/user/.ssh/id_rsa.pem
this is from mine spring application.properties
ok, I generated the keys using ssh-keygen specified public and... the application crashed when trying to connect the key. I suspect that it is not in pem format. After that, I specified the private key (rsa_id), the application started, in the debug it can be seen that the keys were connected, but when authorizing it gives permission denied (public key)
After trying to convert the key to pem
openssl req -x509 -key id_rsa -nodes -days 365 - newkey rsa:2048 -out id_rsa.pem
produces: Key type org.bouncycastle.cert.X509CertificateHolder not supported
In Windows, for keys generated in puttygen, the picture is about the same.
What am I doing wrong?