If your coffee isn’t whipping properly, ensure that you’ve measured all ingredients accurately, as adding too much or too little of a certain ingredient can alter the texture of your dalgona. Remember that it’s important to use a 1:1 ratio of espresso and sugar.
If you’re using the correct amount of each ingredient, your blender may be to blame. Be sure to use a high-quality hand or stand mixer to ensure your whipped coffee doesn’t become too thick or thin.