Yahoo Weather API sometimes works sometimes not

Question

Im developing an APP which is getting the weather time from a query to Yahoo API.

Here is my query maybe it works the first time, but If you refresh the browser maybe it dosnt work.

Here is the documentation

And the limits:

Rate Limits Use of the Yahoo Weather API should not exceed reasonable request volume. Access is limited to 2,000 signed calls per day.

Should I use an API key? or what is the problem? Thanks!