Serial communication slight problem using Wemos D1 R2 and UNO + ThingSpeak

Projects General Guidance
6

Rather than construct the "body" with this line

String body = "api_key="+writeAPIKey+"&field1="+s1+"&field2="+s2+"&field3="+s3;

you can build it up line by line if you replace the line

client.print(body);

with this

    client.print("api_key=");
    client.print(writeAPIKey);
    client.print("&field1=");
    client.print(receivedString[0]);
    //etc

...R