We provide only pkcs8 keys, if you cannot use pkcs8 you can use the pkcs1 encoding, use openssl to convert
The following command was tested on the version 2.6.5
$ openssl version
LibreSSL 2.6.5
When prompet to enter password, don't enter a password, just press the enter or return key on you keyboard
$ openssl pkcs8 -in pkcs1_pk.pem -out pkcs1_pk.pem
Enter Password:
For this private key the result is has follows
$ cat pkcs1_pk.pem
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
https://gist.github.com/etorox/094eb6d22cf83d72218d2d28ff304bc4#file-pkcs8_pk-pem