To access your procedure from the URL, make sure you grant EXECUTE privileges to APEX_PUBLIC_USER by running the command
GRANT EXECUTE ON <PROCEDURE_NAME> TO APEX_PUBLIC_USER;
The URL should be like http://server_name/apex/<schema_name>.<procedure_name>.
If you also have some parameters to pass, the URL should be like http://server_name/apex/<schemaname>.<procedurename>?<PARAMETER1=VALUE>&<PARAMETER2=VALUE>.
Also if you are a DedicatedDB client please make sure the following line is removed from the ORDS configuration: