Query exec:
https://docs.ninox.com/en/api/public-cloud-apis#execute-a-writable-query
 

Query Parameters:
https://docs.ninox.com/en/api/introduction/tables-fields-records
 

Here is an example:
Global Function in Ninox:
function ListRecord() do
    let vTable := (select API_DataTable);
    let vRecords := for i in vTable do
            {
Name: i.Name,
                Zahl: i.Zahl,
                Boolean: i.Boolean,
                dynMultiChoice : text(i.dynMultiChoce),
                functionField : i.functionField,
               date: format(i.date, "MM-DD-YYYY")
            }
        end;
    vRecords
end;

You see, that you get back the value of a function-Field in the Record, which you never get with a simple GET-Request.

Here the http-Request:
let vUrl := "https://Test.ninoxdb.de/v1/teams/d3p8zzk6ytvee6eee/databases/c6s98n6rag10/exec?perPage=10000";
let vHeader := {"Authorization":"Bearer API-KEY","Content-Type":"application/json"};
let vBody := {"query":"ListRecord()"};
do as server
http("POST", vUrl, vHeader, vBody)
end
------------------
?perPage=10000 means, you extend the the get back-limit of 100 Records.

Here is the curl Form.
You can test it here: https://reqbin.com/curl

curl https://Test.ninoxdb.de/v1/teams/d3p8zzk6ytvee6eee/databases/c6s98n6rag10/exec?perPage=10000
-X POST
-H 'Authorization : Bearer API_Key'
-H 'Content-Type : application/json'
-d '{"query":"ListRecord()"}'