signal-cli-rest-api: Unable to receive messages sent to a group

I’m running latest stable home assistant on latest homeassistant os, installed this addon from the repository.

I was able to register a phone number and create a group using the following command:

curl -X POST -H "Content-Type: application/json" -d '{"name": "<group_name>", "members": ["<other_number>"]}' 'http://192.168.0.10:8080/v1/groups/<my_number>'

I am also able to send messages to the group but when I go to the group in Signal, that message is not received.

This is the command I used to send the message to the group:

curl -X POST -H "Content-Type: application/json" -d '{"message": "Testing.", "number": "<my_number>", "recipients": ["<group_id>"]}' 'http://127.0.0.1:8080/v2/send'

By running the command curl -X GET -H "Content-Type: application/json" 'http://127.0.0.1:8080/v1/groups/+61XXXXXXXX', I get the following message for the group:

[{"name":"<name>","id":"<group_id>","internal_id":"<internal_id>","members":["<my_number>] Pending members: [<other_number>] Requesting members: [] Link: -"],"active":true,"blocked":false}]

The other number has accepted the invitation to join the group. Yet, the message is not being received.

Am I missing something here?