I am trying to install/activate an SSL certificate in the Acquia Cloud UI and receive the something along the lines of the following error: "An unknown error occurred. Please try your request again. If the problem persists, Contact Acquia Support. Request Id: XXXX"
If the Root certificate file that is included in the CA intermediate chain is expired OR if the intermediate chain files are out of order, you would likely receive the "unknown error" message.
In order to confirm if the order of your intermediate chain files is correct, please feel free to use the commands provided at option 5 within the following documentation here: Verifying the validity of an SSL certificate.
In order to confirm if your Root certificate file has expired or not, we recommend contacting your Certificate Authority to request either the updated version of the intermediate files or in order to verify the expiration date of your chain.