curl command is not working anymore

[Cerunnos75]

The project was working for me 3 years now. Since 2 months I can't controll via curl request anymore. The web-GUI is working ....
entereing from the comman dpromt, I get the replay "service unavailable".

curl -v -d 'AN:01' 192.168.188.120/api

• Trying 192.168.188.120:80...
• Connected to 192.168.188.120 (192.168.188.120) port 80

POST /api HTTP/1.1
Host: 192.168.188.120
User-Agent: curl/8.4.0
Accept: /
Content-Length: 7
Content-Type: application/x-www-form-urlencoded

< HTTP/1.1 503 Service Unavailable
< Content-Type: text/plain
< Content-Length: 19
< Connection: close
<
Service Unavailable* Closing connection