Unable to integrate Mpesa Api into my android app

Question

I am trying to integrate MPESA API into my android app using the procedures given by Daraja. On launching my application, the following error is displayed in my Logcat

D/OkHttp: {
                    "requestId": "16583-1090909-1",
                    "errorCode": "400.008.02",

D/OkHttp: "errorMessage": "Invalid grant type passed" }

and after entering a Phone number and amount to be sent, the Sim Toolkit is not being brought to the front. The following error is displayed in my Logcat

D/OkHttp: {
                    "requestId":"29178-5342114-1",

D/OkHttp: "errorCode": "404.001.04", "errorMessage": "Invalid Authentication Header" }

This was my expectation: On pressing the "Pay" button, I should be prompted to the sim toolkit requesting for my Mpesa pin to continue with the payment.

I will appreciate any assistance that will be offered.