Issue with Adobe Sign on Mobile Phone and Digital Signs.

ear Support Team,

I am having an issue with Adobe Sign on a mobile phone. I have outlined the steps below:

1. User A opens Adobe Acrobat, either from the computer or from the mobile, and requests a digital signature from user B.
2. B receives a notification on his android mobile through the Acrobat Sign application. When trying to sign, a message appears saying: "A few more steps. To complete the signing, you'll need to go to a Windows or macOS computer, download the agreement, open it in Adobe Acrobat or Acrobat Reader, and provide a digital certificate.". en spanish: "unos pocos pasos mas. Para terminar de firmar, tendrá que ir a un ordenador con Windows o macOS, descargar el acuerdo, abrirlo en Adobe Acrobat o Acrobat Reader y proporcionar un certificado digital".
3. B installs a digital certificate (in his case from the FNMT CA) on the mobile, through the Settings menu > "Biometric data and security" -> Other security settings > Install certificates from SD.
4. B tries to sign again (even restarting the phone) but the same thing happens as in step 2.

I would appreciate any help you can provide.

Thank you.

Dario.