Error: There was a problem accessing Rollbar service. Code: 0 Message: Ignored

[vjandrea]

Created a new project, configured the post_server_item token in the plugin in the PHP part, JS left deactivated.
When I click on "Send test message to Rollbar", i see an error message with the text:

There was a problem accessing Rollbar service.

Code: 0
Message: Ignored

No further detail is given, nothing new is visible in PHP's error log.
Wordpress 6.2.2
Rollbar plugin 2.6.3
Verified on PHP 7.4 and 8.1

Inspecting the request in the browser to https:///index.php?rest_route=/rollbar/v1/test-php-logging, I can see that the payload is:

php_logging_enabled=true
server_side_access_token_container
server_side_access_token=<mytoken>
js_logging_enabled=false
client_side_access_token_container
client_side_access_token
environment=production
logging_level=1
agent_log_location=/var/tmp
allow_exec=true
endpoint=https://api.rollbar.com/api/1/
branch
capture_error_stacktraces=true
code_version
fluent_host=127.0.0.1
fluent_port=24224
fluent_tag=rollbar
handler=blocking
host
include_error_code_context=false
include_exception_code_context=false
capture_ip=true
capture_username=false
capture_email=false
root=<mydocroot>
timeout=3
custom_truncation
report_suppressed=false
use_error_reporting=false
proxy
send_message_trace=false
include_raw_request_body=false
local_vars_dump=true
enable_must_use_plugin=false
restore_all_defaults=Restore all defaults
test_logging

and the response is :

{"code":0,"message":"Ignored"}

Is there a way to see a better detail of what's going on ?