Jet_A_Knight is correct about the IFR plan time.
Any flight you have done under the IFR is what they need here, and not actual IF time.
I have over 2500 hrs planned IFR, but just over 150 hrs of actual instrument time.
Check your logbook carefully and see if you can find all of your IFR flights. I used to keep a separate record of my IFR planned time at the back of my logbook until I reached the required hours.
Also, if that is your only shortfall, I would be applying now so that when you do achieve the requisite hours, that operator will know that you have been keen to work for them for a while, and not just blown through the door on the day your 50 hrs comes up.
Good Luck.