@IraQiOne 

Hello, try to use virtual server and same service port and internal port for the specific device. 

https://www.tp-link.com/support/faq/1721/

After that, you can test whether you can access it with this device's IP address and port number; meanwhile, you can use the WAN IP plus port number to test.

Besides, please use telnet to test:

1. in the same network, please go to run—cmd—telnet lan ip port number 

2. in external network, please run—cmd—telnet wan ip port number

Note: Please show us the pictures of the test results.

Good day.