How can i configure callback in SandBox ?

Hello @allan.ddamulira @Ddamula. I did the steps required but I am not getting any callbacks. Is it working for you?
1- I created an api user with this body: 

{

"providerCallbackHost": "kiab-api-pr-28.onrender.com"

}
2- I generated the apikey.
3-  I created basic authentification with the reference of the API user and the API key.
4- I added this URL to my requestToPay callback url header:
'X-Callback-Url': 'http://localhost:3000/api/mtn'
But this url was never reached, I tried with these values to but it didnt work:
"providerCallbackHost": "localhost:3000"
'X-Callback-Url': 'http://kiab-api-pr-28.onrender.com/api/mtn'
@crankluga @anicet Can you please help me 🤗🤝