Recent versions of OpenSSH (7.8 and newer) generate keys in newOpenSSH format by default, which starts with:
-----BEGIN OPENSSH PRIVATE KEY-----
Some blocks such as the file block configured with an SCP/SFTP sources are not yet compatible with this new format. When a key represented in this format is used,
Omniscope will show an error like this:
Luckily it is possible to convert the key into a format that is supported by Omniscope.
The first step is to create a copy of the original private key. Assuming the key is called id_rsa
cp id_rsa id_rsa.pem
Then using you can convert the key using ssh-keygen:
ssh-keygen -p -f id_rsa.pem -e -m pem
Next click on Conversions -> Export OpenSSH key
Finally reconfigure the Omniscope block to use the new private key file.