When I use flour to thicken chicken broth, I always get lumps. I even used Wonder
Granulated flour same problem. People have told me, the liquid is too hot and I am
Boiling the flour.

Best bet is making a roux with the flour, mixed into butter, to a paste, then add it to your liquid, or mix flour and water using a whisk and beating it until there are no lumps, and if you are still not sure, strain it through a seive. The liquid has to be hot but not boiling while adding the thickener.

However, you can always use corn starch mixed with water and that is foolproof for no lumps but the flavour is different.

Best bet is making a roux with the flour, mixed into butter, to a paste, then add it to your liquid, or mix flour and water using a whisk and beating it until there are no lumps, and if you are still not sure, strain it through a seive. The liquid has to be hot but not boiling while adding the thickener.

However, you can always use corn starch mixed with water and that is foolproof for no lumps but the flavour is different.

Thanks