How to send int array with ESP8266 http post request?
You could use the (awesome) ArduinoJSON library, but likely overkill for this app. I found it more useful to parse JSON than to construct it.
You could simply print to a buffer and the POST that:
char payload[MAX_PAYLOAD];
sprintf(payload, &quot;{\&quot;uid1\&quot;:%d,\&quot;uid2\&quot;:%d,\&quot;uid3\&quot;:%d,\&quot;uid4\&quot;:%d}&quot;, UID[0], UID[1], UID[2], UID[3]);

http.POST(payload);


You would #define MAX_PAYLOAD with a value that will be sufficient to hold all the information.
Notice that sprintf allows you to use any formatting options you want (e.g. hexadecimal, etc).
If you wanted to send it as an array:
sprintf(payload, &quot;{\&quot;uid\&quot;:[%d,%d,%d,%d]}&quot;, UID[0], UID[1], UID[2], UID[3]);