Undefined function 'real' for input arguments of type 'string' Error

So i have been getting this error for quite a long and i don't know whats the problem in the code. Refer to the code, I have to plot the waveform of the data that is stored in the z variable after concatenation of several strings. The point is to get data from 8 different fields of same channel in Thingspeak platform. So far I have received data from the all fields and make a single string of the data. In the end, when I try to plot it prompt me with the following error and does not plot the data.

======> "Undefined function 'real' for input arguments of type 'string' Error" <======

Can somebody please guide me how to remove this error as I am not very familiar with MATLAB coding. Any help will be really appreciated.

data1=thingSpeakRead(readChannelID,'Fields',[1],'NumPoint',1,'OutputFormat','timetable');

data2=thingSpeakRead(readChannelID,'Fields',[2],'NumPoint',1,'OutputFormat','timetable');

data3=thingSpeakRead(readChannelID,'Fields',[3],'NumPoint',1,'OutputFormat','timetable');

data4=thingSpeakRead(readChannelID,'Fields',[4],'NumPoint',1,'OutputFormat','timetable');

data5=thingSpeakRead(readChannelID,'Fields',[5],'NumPoint',1,'OutputFormat','timetable');

data6=thingSpeakRead(readChannelID,'Fields',[6],'NumPoint',1,'OutputFormat','timetable');

data7=thingSpeakRead(readChannelID,'Fields',[7],'NumPoint',1,'OutputFormat','timetable');

data8=thingSpeakRead(readChannelID,'Fields',[8],'NumPoint',1,'OutputFormat','timetable');

L=string(data1.test1);

L1=extractBefore(L,"/");

x1=strsplit(L1,' ');

M=string(data2.test2);

M1=extractBefore(M,"/");

x2=strsplit(M1,' ');

N=string(data3.test3);

N1=extractBefore(N,"/");

x3=strsplit(N1,' ');

O=string(data4.test4);

O1=extractBefore(O,"/");

x4=strsplit(O1,' ');

P=string(data5.test5);

P1=extractBefore(P,"/");

x5=strsplit(P1,' ');

Q=string(data6.test6);

Q1=extractBefore(Q,"/");

x6=strsplit(Q1,' ');

R=string(data7.test7);

R1=extractBefore(R,"/");

x7=strsplit(R1,' ');

S=string(data8.test8);

x8=strsplit(S,' ');

z=cat(2,x1,x2,x3,x4,x5,x6,x7,x8)

thingSpeakPlot(z)