pro attach does not cope well with squid-deb-proxy ACLs

Hello, my 18.04 LTS system has squid-deb-proxy configured, and it does not have esm.ubuntu.com configured in the ACLs in /etc/squid-deb-proxy/mirror-dstdomain.acl.d/ yet. This causes an error that's not exactly obvious:

$ sudo pro attach REDACTED
Enabling default service esm-apps
Enabling default service esm-infra
Enabling default service livepatch
Installing canonical-livepatch snap
Canonical livepatch enabled.
Failed to enable default services, check: sudo pro status
$ sudo pro status
SERVICE ENTITLED STATUS DESCRIPTION
cc-eal yes disabled Common Criteria EAL2 Provisioning Packages
cis yes disabled Security compliance and audit tools
esm-infra yes disabled Expanded Security Maintenance for Infrastructure
fips yes disabled NIST-certified core packages
fips-updates yes disabled NIST-certified core packages with priority security updates
livepatch yes enabled Canonical Livepatch service

Enable services with: pro enable <service>

                Account: Canonical - staff
           Subscription: Ubuntu Pro (Apps-only)
            Valid until: Fri Dec 31 15:59:59 3999 PST
Technical support level: essential
$ sudo pro enable esm-infra
One moment, checking your subscription first
Unexpected APT error. See /var/log/ubuntu-advantage.log

The ubuntu-advantage.log does have sufficient details to debug the problem. I'm just curious if there's anything we can do here to give a hint without resorting to the log. (Maybe report if apt is configured to use a proxy? I'm really not sure what I'm expecting.)

Thanks

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-advantage-tools 27.11.2~18.04.1
ProcVersionSignature: Ubuntu 4.15.0-188.199-generic 4.15.18
Uname: Linux 4.15.0-188-generic x86_64
NonfreeKernelModules: lkp_Ubuntu_4_15_0_188_199_generic_89 zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.9-0ubuntu7.28
Architecture: amd64
Date: Wed Oct 5 18:37:33 2022
InstallationDate: Installed on 2012-10-18 (3639 days ago)
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
ProcEnviron:
 LC_TIME=C
 TERM=rxvt-unicode-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-advantage-tools
UpgradeStatus: Upgraded to bionic on 2018-05-02 (1618 days ago)