org.springframework.web.client.ResourceAccessException: I/O error on POST request for "https://api.openai.com/v1/completions": Connection timed out: connect; nested exception is java.net.ConnectException: Connection timed out: connect
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:785) ~[spring-web-5.3.19.jar:5.3.19]
It seems your jar application can not access openai.
I guess that Ajax accesses openai using the browser proxy, but your jar application does not use it.
org.springframework.web.client.ResourceAccessException: I/O error on POST request for "https://api.openai.com/v1/completions": Connection timed out: connect; nested exception is java.net.ConnectException: Connection timed out: connect at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:785) ~[spring-web-5.3.19.jar:5.3.19]