fix: GSTR 3b report fixes (#17317)

* fix: GSTR-3b report total taxable value fixes

* fix: Test Cases
diff --git a/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py b/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
index a9aa1d5..7faabf4 100644
--- a/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
+++ b/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
@@ -227,12 +227,18 @@
 
 		for d in inter_state_supply.get("Unregistered", []):
 			self.report_dict["inter_sup"]["unreg_details"].append(d)
+			self.report_dict["sup_details"]["osup_det"]["txval"] += d["txval"]
+			self.report_dict["sup_details"]["osup_det"]["iamt"] += d["iamt"]
 
 		for d in inter_state_supply.get("Registered Composition", []):
 			self.report_dict["inter_sup"]["comp_details"].append(d)
+			self.report_dict["sup_details"]["osup_det"]["txval"] += d["txval"]
+			self.report_dict["sup_details"]["osup_det"]["iamt"] += d["iamt"]
 
 		for d in inter_state_supply.get("UIN Holders", []):
 			self.report_dict["inter_sup"]["uin_details"].append(d)
+			self.report_dict["sup_details"]["osup_det"]["txval"] += d["txval"]
+			self.report_dict["sup_details"]["osup_det"]["iamt"] += d["iamt"]
 
 	def get_total_taxable_value(self, doctype, reverse_charge):
 
@@ -296,7 +302,7 @@
 
 			inter_state_supply_details[d.gst_category].append({
 				"pos": get_state_code(d.gst_state),
-				"txval": d.total,
+				"txval": d.total - d.tax_amount,
 				"iamt": d.tax_amount
 			})
 
diff --git a/erpnext/regional/doctype/gstr_3b_report/test_gstr_3b_report.py b/erpnext/regional/doctype/gstr_3b_report/test_gstr_3b_report.py
index d50eaeb..4667107 100644
--- a/erpnext/regional/doctype/gstr_3b_report/test_gstr_3b_report.py
+++ b/erpnext/regional/doctype/gstr_3b_report/test_gstr_3b_report.py
@@ -57,7 +57,7 @@
 
 		output = json.loads(report.json_output)
 
-		self.assertEqual(output["sup_details"]["osup_det"]["iamt"], 18),
+		self.assertEqual(output["sup_details"]["osup_det"]["iamt"], 36),
 		self.assertEqual(output["sup_details"]["osup_zero"]["iamt"], 18),
 		self.assertEqual(output["inter_sup"]["unreg_details"][0]["iamt"], 18),
 		self.assertEqual(output["sup_details"]["osup_nil_exmp"]["txval"], 100),