There is such a mountain of mis-information concerning versions of java, certificates and installation, I'm amazed anyone gets anywhere near. In fact, they don't. They go to a gestor or to the bank to get someone else who doesn't need to use a certificate to prove who they are to do it for them.
Anyway, here's what works using kubuntu 20.04
- Make sure you have the AutoFirma .dpkg installed.
- Make sure the certificates are in place:
- Export your personal certificate.
- Hit the 'pagar y firmar' button on your selected page.
- In the popup, choose your exported certificate:
- Check they are your details and hit OK:
That's it.
Elegant? No. Works? Yes.