This actually should work. You just need to copy the content of the pem file to the private part of the key when copying it into Termius app in the Keychain section.
We’ll double-check it.
If you have any other problems please contact us here – http://support.termius.com/
This doesn’t directly answer the question here but I can describe the successful process I used to be able to setup Termius on an iPad to access an AWS instance.
First create an RSA key in Termius. The type must be RSA, size can be anything and you can add a pass phrase if you like. Next you need to ‘Copy Public Key’.
Now go to your AWS console. Under Network & Security > Key Pairs click the ‘Import Key Pair’ button. Give the key a name and paste the public key in the large text box.
Now, still in the AWS console create your instance. When setting up security use the key you just added. Make a note of the instance details (username & hostname).
Back in Termius add the host with the noted details. Remember to setup the host to use the key you created.
That’s it. You should be able to log in now. At least I was when using this process.