Baking cake dilemma!!

[AllHopeAndNoResults]

Can anyone help me out! What am I doing wrong?
I am not a baker, I’ve probablt baked about 4 successful cakes in my life. Today I tried to do the simplest of all sponge cakes in an electric oven (may be relevant) the middle sinks and it’s tasting metallic. I followed an easy recipe online to the word and tried this 3 times today. What am I doing wrong?

If it sinks it's underbaked anyway, leave it in a bit longer. When you can smell the baked cake gently open the door, test the cake with a metal skewer or thin knife if it doesn't come out clean close the door gently again for a few more mins. No idea on the metal taste!

Did you manage to solve the problem? What was the recipe?