arduino - How to detect 220 VAC voltage using an opto-isolator

I created the following circuit.

I plugged it in and it works!!

Now I thought of adding an opto-isolator to the circuit in place of the LED. The value of C was the same.

$$ X_c = {(({220volts-1.4volts})/0.01A))} = {(2*π*(50Hz)*C)}^{-1} $$

$$ solve for :C=150nF $$

so I ended up with the circuit below.

The two diodes in series are actually present and on the first circuit to achieve a drop-down of 1.4 volts same as the external LED and for the internal LED.

The opto-isolator used was ln4n25

The diodes are proper voltage rating. Why a drop down of 0.7 volts

The problem is that gate of the transistor is not getting high when connected to mains. Meaning that the internal LED is off so GPIO is always HIGH.

Any thoughts? Is the internal LED even turning on? How can I check?

Also I currently have access to this and only this opto-isolator.