I have ubuntu server arm64 22.04 running on a raspberry pi for use as a wifi hotspot with the internet connection provided by a cellular modem. I'm using networkmanager and modemmanager to manage the connections. All packages are updated.

I have been able to create a wifi hotspot using nmcli and I can connect other devices to it but the connected devices stay on "self assigned ip" and do not get an ip address, router, or subnet mask. At the time of testing I have not yet set up the modem since I need the usb port for ssh until i get the hotspot working.

dnsmasq is already installed because I needed it to enable usb-gadget mode so I can ssh into the rpi. Following the instructions here (https://lozworld.com/lozwords/raspberry-pi-4b-as-an-ubuntu-2110-usb-gadget-tethered-to-an-ipad-pro) I made the following configuration changes:
/etc/dnsmasq.d/usb:

interface=usb0

dhcp-range=10.55.0.2,10.55.0.6,255.255.255.248,1h

dhcp-option=3

leasefile-ro

port=0

/etc/default/dnsmasq:

DNSMASQ_EXCEPT="lo"

Here are the commands I used to create the hotspot:

nmcli con add type wifi ifname wlan0 con-name Hostspot autoconnect yes ssid Hostspot

nmcli con modify Hostspot 802-11-wireless.mode ap 802-11-wireless.band bg ipv4.method shared

nmcli con modify Hostspot wifi-sec.key-mgmt wpa-psk

nmcli con modify Hostspot wifi-sec.psk "veryveryhardpassword1234"

nmcli con up Hostspot

When the hotspot nmcli connection is up, running systemctl restart dnsmasq.service returns

Jul 22 16:01:04 raspberrypi systemd[1]: Starting dnsmasq - A lightweight DHCP and caching DNS server...

Jul 22 16:01:04 raspberrypi dnsmasq[1722]: dnsmasq: failed to bind DHCP server socket: Address already in use

Jul 22 16:01:04 raspberrypi dnsmasq[1722]: failed to bind DHCP server socket: Address already in use

Jul 22 16:01:04 raspberrypi dnsmasq[1722]: FAILED to start up

Jul 22 16:01:04 raspberrypi systemd[1]: dnsmasq.service: Control process exited, code=exited, status=2/INVALIDARGUMENT

Jul 22 16:01:04 raspberrypi systemd[1]: dnsmasq.service: Failed with result 'exit-code'.

Jul 22 16:01:04 raspberrypi systemd[1]: Failed to start dnsmasq - A lightweight DHCP and caching DNS server.

Here is the output of "nmcli con show":

connection.id:                          Hotspot

connection.uuid:                        afbf8081-cb19-4d5e-8517-38c222607984

connection.stable-id:                   --

connection.type:                        802-11-wireless

connection.interface-name:              wlan0

connection.autoconnect:                 yes

connection.autoconnect-priority:        0

connection.autoconnect-retries:         -1 (default)

connection.multi-connect:               0 (default)

connection.auth-retries:                -1

connection.timestamp:                   1658497260

connection.read-only:                   no

connection.permissions:                 --

connection.zone:                        --

connection.master:                      --

connection.slave-type:                  --

connection.autoconnect-slaves:          -1 (default)

connection.secondaries:                 --

connection.gateway-ping-timeout:        0

connection.metered:                     unknown

connection.lldp:                        default

connection.mdns:                        -1 (default)

connection.llmnr:                       -1 (default)

connection.dns-over-tls:                -1 (default)

connection.wait-device-timeout:         -1

802-11-wireless.ssid:                   horsies

802-11-wireless.mode:                   ap

802-11-wireless.band:                   bg

802-11-wireless.channel:                0

802-11-wireless.bssid:                  --

802-11-wireless.rate:                   0

802-11-wireless.tx-power:               0

802-11-wireless.mac-address:            --

802-11-wireless.cloned-mac-address:     --

802-11-wireless.generate-mac-address-mask:--

802-11-wireless.mac-address-blacklist:  --

802-11-wireless.mac-address-randomization:default

802-11-wireless.mtu:                    auto

802-11-wireless.seen-bssids:            E4:5F:01:97:CB:A2

802-11-wireless.hidden:                 no

802-11-wireless.powersave:              0 (default)

802-11-wireless.wake-on-wlan:           0x1 (default)

802-11-wireless.ap-isolation:           -1 (default)

802-11-wireless-security.key-mgmt:      wpa-psk

802-11-wireless-security.wep-tx-keyidx: 0

802-11-wireless-security.auth-alg:      --

802-11-wireless-security.proto:         --

802-11-wireless-security.pairwise:      --

802-11-wireless-security.group:         --

802-11-wireless-security.pmf:           0 (default)

802-11-wireless-security.leap-username: --

802-11-wireless-security.wep-key0:      <hidden>

802-11-wireless-security.wep-key1:      <hidden>

802-11-wireless-security.wep-key2:      <hidden>

802-11-wireless-security.wep-key3:      <hidden>

802-11-wireless-security.wep-key-flags: 0 (none)

802-11-wireless-security.wep-key-type:  unknown

802-11-wireless-security.psk:           <hidden>

802-11-wireless-security.psk-flags:     0 (none)

802-11-wireless-security.leap-password: <hidden>

802-11-wireless-security.leap-password-flags:0 (none)

802-11-wireless-security.wps-method:    0x0 (default)

802-11-wireless-security.fils:          0 (default)

ipv4.method:                            shared

ipv4.dns:                               --

ipv4.dns-search:                        --

ipv4.dns-options:                       --

ipv4.dns-priority:                      0

ipv4.addresses:                         --

ipv4.gateway:                           --

ipv4.routes:                            --

ipv4.route-metric:                      -1

ipv4.route-table:                       0 (unspec)

ipv4.routing-rules:                     --

ipv4.ignore-auto-routes:                no

ipv4.ignore-auto-dns:                   no

ipv4.dhcp-client-id:                    --

ipv4.dhcp-iaid:                         --

ipv4.dhcp-timeout:                      0 (default)

ipv4.dhcp-send-hostname:                yes

ipv4.dhcp-hostname:                     --

ipv4.dhcp-fqdn:                         --

ipv4.dhcp-hostname-flags:               0x0 (none)

ipv4.never-default:                     no

ipv4.may-fail:                          yes

ipv4.required-timeout:                  -1 (default)

ipv4.dad-timeout:                       -1 (default)

ipv4.dhcp-vendor-class-identifier:      --

ipv4.dhcp-reject-servers:               --

ipv6.method:                            auto

ipv6.dns:                               --

ipv6.dns-search:                        --

ipv6.dns-options:                       --

ipv6.dns-priority:                      0

ipv6.addresses:                         --

ipv6.gateway:                           --

ipv6.routes:                            --

ipv6.route-metric:                      -1

ipv6.route-table:                       0 (unspec)

ipv6.routing-rules:                     --

ipv6.ignore-auto-routes:                no

ipv6.ignore-auto-dns:                   no

ipv6.never-default:                     no

ipv6.may-fail:                          yes

ipv6.required-timeout:                  -1 (default)

ipv6.ip6-privacy:                       -1 (unknown)

ipv6.addr-gen-mode:                     stable-privacy

ipv6.ra-timeout:                        0 (default)

ipv6.dhcp-duid:                         --

ipv6.dhcp-iaid:                         --

ipv6.dhcp-timeout:                      0 (default)

ipv6.dhcp-send-hostname:                yes

ipv6.dhcp-hostname:                     --

ipv6.dhcp-hostname-flags:               0x0 (none)

ipv6.token:                             --

proxy.method:                           none

proxy.browser-only:                     no

proxy.pac-url:                          --

proxy.pac-script:                       --

GENERAL.NAME:                           Hotspot

GENERAL.UUID:                           afbf8081-cb19-4d5e-8517-38c222607984

GENERAL.DEVICES:                        wlan0

GENERAL.IP-IFACE:                       wlan0

GENERAL.STATE:                          activated

GENERAL.DEFAULT:                        no

GENERAL.DEFAULT6:                       no

GENERAL.SPEC-OBJECT:                    /org/freedesktop/NetworkManager/AccessPoint/60

GENERAL.VPN:                            no

GENERAL.DBUS-PATH:                      /org/freedesktop/NetworkManager/ActiveConnection/20

GENERAL.CON-PATH:                       /org/freedesktop/NetworkManager/Settings/1

GENERAL.ZONE:                           --

GENERAL.MASTER-PATH:                    --

IP4.ADDRESS[1]:                         10.42.0.1/24

IP4.GATEWAY:                            --

IP4.ROUTE[1]:                           dst = 10.42.0.0/24, nh = 0.0.0.0, mt = 600

IP6.ADDRESS[1]:                         fe80::7d33:50b:86ba:ca37/64

IP6.GATEWAY:                            --

IP6.ROUTE[1]:                           dst = fe80::/64, nh = ::, mt = 1024