JSF(Primefaces) ajax update of several elements by ID's
If the to-be-updated component is not inside the same NamingContainer component (ui:repeat, h:form, h:dataTable, etc), then you need to specify the "absolute" client ID. Prefix with : (the default NamingContainer separator character) to start from root.
<p:ajax process="@this" update="count :subTotal"/>To be sure, check the client ID of the subTotal component in the generated HTML for the actual value. If it's inside for example a h:form as well, then it's prefixed with its client ID as well and you would need to fix it accordingly.
<p:ajax process="@this" update="count :formId:subTotal"/>Space separation of IDs is more recommended as <f:ajax> doesn't support comma separation and starters would otherwise get confused.