[SOLVED] Matrix Synapse no longer working, update error "matrix-synapse is kept back"

I tried recently to connect from my Freedombox to another server and it appears I can no longer do so (I did in the past, before the manual update above). For example, if I try to join a known room #ROOM:SERVER.org, I get the error:

#ROOM:SERVER.org is not accessible at this time.

Try again later, or ask a room or space admin to check if you have access.

M_UNKNOWN was returned while trying to access the room or space. If you think you’re seeing this message in error, please submit a bug report.

I suspect it may have to do with this:

The name that this homeserver will appear as, to clients and other servers via federation. This name should match the SRV record published in DNS. Name of the server: ____

As I noted above, when I received the above prompt I put the Domain Name found under System > Dynamic DNS Client (e.g., NAME.freedombox.rocks).

Is it possible I should have written something else?

Other ideas about what the federation issue I am having is caused by?

Thank you!