External providers can now be loaded

Implemented invoice protocol (see docs)

src/models/invoice/invoice.interface.ts

@@ -29,7 +29,7 @@ export interface IInvoice extends Document {
 
     // Is set when invoice got paid
     // 3b38c3a215d4e7981e1516b2dcbf76fca58911274d5d55b3d615274d6e10f2c1
-    transcationHashes?: string;
+    transcationHash?: string;
 
     cart?: ICart[];
     totalPrice?: number;