https request in Oracle 18c : "ORA-29024: Certificate validation failure" - plsql

Question

I use Oracle 18C pl sql script.
I would like to make https requests.
So, i begin with http requests and it works. But, with https requests, i have an error : "Certificate validation failure".
I will explain below how I proceed in order to reach "https://www.ibm.com" for example.
I create a wallet using this powershell script :
Get-ChildItem -Path Z:\Documents\dev\plsql_http_request\wallets -Include *.* -File -Recurse | foreach { $_.Delete()}
orapki wallet create -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000 -auto_login
orapki wallet add -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000 -trusted_cert -cert 'Z:\Documents\dev\plsql_http_request\certificates\ibm-1-root.pem'
orapki wallet add -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000 -trusted_cert -cert 'Z:\Documents\dev\plsql_http_request\certificates\ibm-2-intermediate.pem'
orapki wallet add -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000 -trusted_cert -cert 'Z:\Documents\dev\plsql_http_request\certificates\ibm-3-user.pem'
orapki wallet display -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000
Certificates are in PEM base64 format.
I have this output from this command orapki wallet display -wallet Z:\Documents\dev\plsql_http_request\wallets -pwd iciC29000 :
Requested Certificates:
User Certificates:
Trusted Certificates:
Subject: CN=www.ibm.com,O=International Business Machines Corporation,L=Armonk,ST=NEW YORK,C=US
Subject: CN=DigiCert Global Root CA,OU=www.digicert.com,O=DigiCert Inc,C=US
Subject: CN=DigiCert TLS RSA SHA256 2020 CA1,O=DigiCert Inc,C=US
Then, I modify rights of the wallet file : file permissions
Then, i execute this pl/sql script :
set serveroutput on size 30000;
declare
v_req utl_http.req;
v_res utl_http.resp;
v_buffer varchar2(4000);
begin
UTL_HTTP.set_detailed_excp_support ( TRUE );
utl_http.set_wallet('file:Z:\Documents\dev\plsql_http_request\wallets\','iciC29000');
v_req := utl_http.begin_request('https://www.ibm.com');
v_res := utl_http.get_response(v_req);
utl_http.read_text(v_res, v_buffer, NULL);
utl_http.end_response(v_res);
dbms_output.put_line(v_res.status_code);
dbms_output.put_line(v_res.reason_phrase);
dbms_output.put_line(v_buffer);
end;
And now, i'm stucked with these errors :
Error report -
ORA-29024: Certificate validation failure
ORA-06512: at "SYS.UTL_HTTP", line 380
ORA-06512: at "SYS.UTL_HTTP", line 1148
ORA-06512: at line 15
29024. 00000 - "Certificate validation failure"
*Cause: The certificate sent by the other side could not be validated. This may occur if
the certificate has expired, has been revoked, or is invalid for another reason.
*Action: Check the certificate to determine whether it is valid. Obtain a new certificate,
alert the sender that the certificate has failed, or resend.
Thanks a lot for your help.