PA-28 instructor pilot with trainee reported descending below the initial approach altitude after misreading the approach chart.

Narrative

I was with my student on a training flight to ZZZ; departing from ZZZ1; our objective was to practice the RNAV XX; circling to Runway XY. The weather conditions at ZZZ were 900 overcast with 10sm of visibility. After passing the initial approach fix (ZZZZZ); I advised the student to descend to 2000 feet msl to meet our final approach fix (ZZZZZ1). During descent we were alerted with a 'LOW ALT' CAS message on our G1000. I then realized we had descended past the intended 2400 minimums required altitude from our IAF to our FAF; to 2100. I immediately advised my student to begin climbing back to 2400 as we were intending for 2000.After recovering back to 2400 I noticed what caused my mistake. Having filed our flight plan IFR I had my expected route loaded in Foreflight. I was using the Jeppesen chart map overlay feature on my iPad and the intended route partially covered the '4' of the '2400' minimum altitude route noted on the approach plate.I believe this was a result of complacency. Our airport had previously been experiencing an extended period of south flow days and in training Instrument; our main approach back into the airport brings us down to 2000 feet to the Final Approach fix. I believe having done the approach multiple times; I believe I got stuck from expectancy bias and that is what caused me telling my student to descend to 2000.Getting back to the airport; I immediately requested an IFR Currency Simulator session to practice briefing approaches and retraining the scenario to see how I can do better.