Ubuntu 24.04, postfix and spamassassin

I was running Ubuntu 23.04, with postfix, with spamassassin installed as a service with systemctl. At the weekend I upgraded the distro to 24.04 and have now discovered that postfix is no longer able to call spamassassin. Originally I followed this installation guide: https://www.linuxbabe.com/mail-server/block-email-spam-check-header-body-with-postfix-spamassassin It configures /etc/postfix/main.cf with this milter: smtpd_milters = local:spamass/spamass.sock I now get these errors at various times:

mail:/w/serverless# cat /var/log/mail.log.1 | grep spam

Jul  6 15:33:49 mail spamass-milter: spamass-milter 0.4.0 starting
Jul  6 15:34:40 mail spamass-milter: Could not retrieve sendmail macro "b"!.  Please add it to confMILTER_MACROS_ENVRCPT for better spamassassin results
2024-07-06T16:10:54.054537+02:00 mail spamass-milter: spamass-milter 0.4.0 starting
2024-07-06T20:45:21.391844+02:00 mail spamass-milter: Could not retrieve sendmail macro "b"!.  Please add it to confMILTER_MACROS_ENVRCPT for better spamassassin results
2024-07-06T20:45:23.465636+02:00 mail spamass-milter: Could not extract score from 

2024-07-06T23:20:55.566449+02:00 mail spamc: connect to spamd on ::1 failed, retrying (#1 of 3): Connection refused
2024-07-06T23:20:55.566535+02:00 mail spamc: connect to spamd on 127.0.0.1 failed, retrying (#1 of 3): Connection refused
2024-07-06T23:20:56.566720+02:00 mail spamc: connect to spamd on ::1 failed, retrying (#2 of 3): Connection refused
2024-07-06T23:20:56.566814+02:00 mail spamc: connect to spamd on 127.0.0.1 failed, retrying (#2 of 3): Connection refused
2024-07-06T23:20:57.567154+02:00 mail spamc: connect to spamd on ::1 failed, retrying (#3 of 3): Connection refused
2024-07-06T23:20:57.567279+02:00 mail spamc: connect to spamd on 127.0.0.1 failed, retrying (#3 of 3): Connection refused
2024-07-06T23:20:57.567368+02:00 mail spamc: connection attempt to spamd aborted after 3 retries

How can I fix this, and make postfix connect to spamassassin, when it is not running as a service?