Web request returns "ORA-01031: insufficient privileges" on OCI AutonomousDB

Question

I am trying to set up a small Rest API and connect to it from an OCI Autonomous DB. But I am stuck.

This request works:

SELECT apex_web_service.make_rest_request(
p_url => 'https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson'||CHR(38)||'limit=100',
p_http_method => 'GET') JSON
FROM DUAL;

This is a call to an existing public Rest-API (not mine).

This does not work:

SELECT apex_web_service.make_rest_request(
p_url => 'https://raspi.brima.dynv6.net:1880/gettest',
p_http_method => 'GET') JSON
FROM DUAL;

This is my own API. It's only a "Hello World!" example. It is https, because that's a requirement for OCI, but it is not password protected or anything. You should be able to reach it from your browser. So, it is not a "private endpoint", right?

For this call, I get:

ORA-29273: HTTP request failed
ORA-06512: at "APEX_210200.WWV_FLOW_WEB_SERVICES", line 1182
ORA-06512: at "APEX_210200.WWV_FLOW_WEB_SERVICES", line 782
ORA-01031: insufficient privileges
ORA-06512: at "SYS.UTL_HTTP", line 380
ORA-06512: at "SYS.UTL_HTTP", line 1209

The same happens when I try to do the request via UTL_HTTP.

I setup an ACE for Host '*.brima.dynv6.net' and port 1880 for my current DB user with privilege CONNECT and RESOLVE, but that did not change anything. Here the output of DBA_HOST_ACLS and DBA_HOST_ACES as JSON:

[
{"host":"raspi.brima.dynv6.net","acl":"NETWORK_ACL_E05BF60BBE2A22C1E0535318000AF6E5","aclid":"0000000080002750","acl_owner":"SYS","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"*","acl":"NETWORK_ACL_9D275AE6BBA22013E0530F86E50AB596","aclid":"0000000080002724","acl_owner":"SYS","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"raspi.brima.dynv6.net","lower_port":1880,"upper_port":1880,"acl":"NETWORK_ACL_E056B33BAFFC275BE0535318000A1197","aclid":"000000008000274F","acl_owner":"SYS","use_dns_proxy":"N\/A","private_target":"NO"}
]

[
{"host":"*","ace_order":1,"grant_type":"GRANT","inverted_principal":"NO","principal":"GSMADMIN_INTERNAL","principal_type":"DATABASE","privilege":"RESOLVE","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"*","ace_order":2,"grant_type":"GRANT","inverted_principal":"NO","principal":"GGSYS","principal_type":"DATABASE","privilege":"RESOLVE","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"*","ace_order":3,"grant_type":"GRANT","inverted_principal":"NO","principal":"C##OMLREST2","principal_type":"DATABASE","privilege":"RESOLVE","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"raspi.brima.dynv6.net","ace_order":1,"grant_type":"GRANT","inverted_principal":"NO","principal":"SMARTHOME","principal_type":"DATABASE","privilege":"RESOLVE","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"*","ace_order":3,"grant_type":"GRANT","inverted_principal":"NO","principal":"C##OMLREST2","principal_type":"DATABASE","privilege":"CONNECT","use_dns_proxy":"N\/A","private_target":"NO"}
,{"host":"raspi.brima.dynv6.net","lower_port":1880,"upper_port":1880,"ace_order":1,"grant_type":"GRANT","inverted_principal":"NO","principal":"SMARTHOME","principal_type":"DATABASE","privilege":"CONNECT","use_dns_proxy":"N\/A","private_target":"NO"}
]

Also, why is the first example working without a special ACL configuration?

I don't understand the problem. I already looked at this question, but it wasn't really answered.

Can anyone point me in the right direction?

Thanks & Regards, Nadine