moistureData was not empty so alertBody did not get assigned to, but the urlwrite failed because alertBody is not defined so the catch was executed.
Also you need to replace the or in while test with || because or spelled out can only be used in function call form, not as an operator.
Also you need to replace the while with if because otherwise you have an infinite loop. On the other hand temp is not defined. Perhaps you want different logic there??
I have to wonder if you want to send an alert st all if you received data? Perhaps if you did receive data you want to go through the data you received and create an alert if needed? Your current code does the while only if data is empty; perhaps it should be only if the data is received?
Perhaps you should initialize alertBody to '' and have
if ~isempty(alertBody) around the try/catch?
