You can add this script to you configuration and it will run in the background waiting for http-get-request to

https://[phoneIp]/api/v1/exec/interactive.lua

The phone uses tokens to verify http-requests from outside the Web-UI. You can generate such tokens in the Web-UI under Access. Use such a token either as value of an http-header named Authorization or pass it as query-parameter. E.g. (if token is abcefg):

curl -k -H "Authorization: Bearer abcdefg" -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua" -d 'system.toast("hello world")'
curl -k -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua?AuthToken=abcdefg" -d 'system.toast("hello world")'

The body of these http-get-request is expected to hold a lua-script or single lua line that you want to execute. Use return in your script if you want get some information back. E.g.:

curl -k -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua?AuthToken=abcdefg" -d 'return sip.calls.get_all()[1]:getState()'
HTTP/1.1 200 OK
...
Content-Type: text/plain
 
active

Local variables only exist during one http-script execution. They'll be lost when you send the next script. You can create variables in the global namespace, you might want to create a dictionary though, as to not pollute it to much

curl -k -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua?AuthToken=abcdefg" -d '
> local forgetful = 42
> userdata = {}
> userdata.rememberMe = 42
> '
HTTP/1.1 200 OK
...
Content-Type: text/plain
 
 
curl -k -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua?AuthToken=abcdefg" -d 'return forgetful'
HTTP/1.1 200 OK
...
Content-Type: text/plain
 
 
curl -k -i "https://[yourPhonesIp]/api/v1/exec/interactive.lua?AuthToken=abcdefg" -d 'return userdata.rememberMe'
HTTP/1.1 200 OK
...
Content-Type: text/plain
 
42