I got a 3rd Pfizer shot today, here is how it works.
The CDC is not really encouraging this booster. They have a list of very specific medical problems and they don't clearly extend the list to problems related to liver disease so if you are part of this community you have to read between the lines.
Like all government operations, there is the fine print. In this case, after a specific scary list with some vagueness, they provide an option for the patient to state that they belong to an approved group but they do not require proof. Very official documents and all the trimmings but if you state that you are immune-compromised with liver disease most pharmacists are going to give you the shot.
The pharmacy will connect directly to Medicare for payment so be aware that you are making a statement about your medical condition directly to the government. In my case, I know that I did not make antibodies well in the first rounds. I have been tested as part of a trial. Since you belong to this group you likely have immunity risks but you probably don't have specifics. You have to be prepared to say that you are immune compromised if you go this route and seek the booster.
At some point, I expect they will extend the definition to include us more specifically. Our immune systems are frequently compromised but they don't allow testing so it leaves us in a difficult situation if we wish to get the booster.
It is an odd situation, they are begging everyone to get vaccinated but making it difficult for those of us who believe we need the vaccine to get it.