Convert http payload to string for debugging - string

Question

I am using this C++ code on an ESP8266 to check on several http accessible data. Once in a while this device acts strangelay and I would like to be able to look at the data it gets. So I collect all payloads to be able to check it via rest api. The following code ALMOST works
String payloadAll = "start ###";
http.begin(client, getLink2);
httpCode = http.GET();
if ( httpCode > 0 ) { payload = http.getString(); payloadAll = payloadAll + payload.c_str() + "### ENDE-PAYLOAD1 ###"; }
the output looks like this:
start ###Internals: DEF 1 60 192.168.40.1:1502 TCP DeviceName 192.168.40.1:1502 EXPECT idle FD 6 FUUID 5xxxxx-fxxx-9xxx-fxxx-exxxxxxxxxxx IODev SolarEdge Interval 60 LASTOPEN 1647580317.55657 MODBUSID 1 MODE master MODEL SE8K-XXXXXXXXXX### ENDE-PAYLOAD1 ###
That is the first line of the payload only. I don't know much about the formast the requested data is in but once it is in the String, I can search ind find keyword and such from the lines I don't see in the output, so I know the data is there. If I leave out the ".c_str()" part, I will only get "start ###### ENDE-PAYLOAD1 ###"
How can I get all the lines - formatting is not important - it can all be one line, I just need to be able to see it as plain text.
Thanks!