Good news! Your i-Credit 400 meter is compatible with the Powerpal.
The pulse rate to enter into the app is 1600 and you can use the triangular bracket to fit your meter.
Simply fit the bracket into the nook at the bottom left of the display so you can see the red light marked in the photo below flashing through the hole in the bracket.
Once the bracket is attached to the meter face you can then gently twist your Powerpal's sensor clockwise into place.
Then head to https://www.powerpal.net/install and follow the instructions to complete your installation.
