Is IEX300RQ1 correct or should it be IEX3000RQ1?

Here is your parts breakdown
Model IEX3000RQ1

Here is your wiring diagram
https://www.servicematters.com/d...0Sheet%20-%208576793.pdf

The most common causes for no heat are the heater or the thermal cutoff (Item 6 in Section 1).

The best way to check is with a meter.
If you do not have one I would suggest you purchase one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.

If you do not have a meter and do not want to purchase one, pull the heater and check it visually for a break.
The cut off can be checked by shorting the wires together, taping them up so they cannot touch the frame and giving it a try. If it fixes the problem replace it ASAP as this is a safety device.

If it is the thermal cutoff be sure to clean/check your vent system.
Also the lint filter. If you use liquid fabric softener it can coat the screen greatly reducing air flow.

Remember to always unplug or remove power from the unit when working on it.
240 Volts can kill!!!