parse error: asn1: syntax error: sequence truncated

Hello im trying to fetch a google api token for the postmaster tools but i have some errors using the script;

using it directly with the credentials.json download from the google console i have received;

$ ./oauth2l fetch --credentials credentials.json --scope postmaster.readonly
missing 'type' field in credentials
$

Adding "type":"service_account","web" to the json file the error have changed for the following;

$ ./oauth2l fetch --credentials credentials.json --scope postmaster.readonly
private key should be a PEM or plain PKCS1 or PKCS8; parse error: asn1: syntax error: sequence truncated
$

Whats about is the last one related ?,

Thanks