Postman is the best option as suggested in some discussions on this forum.
Or you can try it out on the swagerUI provided by zatca.
So far I have tried it through swagerUI, to understand how eInvoice works. I also don’t really understand using Postman. 
i checked the signed XML Invoice , everytihing seems to be normal and the texts in Arabic are correct :
however, when i try with swagerUI , i’m getting this . not sure if i did things correctly .
Read User Manual Developer Portal,
you should add Basic Authorization for Reporting and Clearance
