fix: Minor fix in GSTR-1 report (#18797)

diff --git a/erpnext/regional/report/gstr_1/gstr_1.py b/erpnext/regional/report/gstr_1/gstr_1.py
index 2da1085..c397133 100644
--- a/erpnext/regional/report/gstr_1/gstr_1.py
+++ b/erpnext/regional/report/gstr_1/gstr_1.py
@@ -156,33 +156,21 @@
 
 
 		if self.filters.get("type_of_business") ==  "B2B":
-			customers = frappe.get_all("Customer",
-				filters={
-					"gst_category": ["in", ["Registered Regular", "Deemed Export", "SEZ"]]
-			})
-
-			if customers:
-				conditions += """ and ifnull(gst_category, '') != 'Overseas' and is_return != 1
-					and customer in ({0})""".format(", ".join([frappe.db.escape(c.name) for c in customers]))
+			conditions += "and ifnull(gst_category, '') in ('Registered Regular', 'Deemed Export', 'SEZ') and is_return != 1"
 
 		if self.filters.get("type_of_business") in ("B2C Large", "B2C Small"):
 			b2c_limit = frappe.db.get_single_value('GST Settings', 'b2c_limit')
 			if not b2c_limit:
 				frappe.throw(_("Please set B2C Limit in GST Settings."))
 
-		customers = frappe.get_all("Customer",
-			filters={
-				"gst_category": ["in", ["Unregistered"]]
-		})
-
 		if self.filters.get("type_of_business") ==  "B2C Large" and customers:
 			conditions += """ and SUBSTR(place_of_supply, 1, 2) != SUBSTR(company_gstin, 1, 2)
-				and grand_total > {0} and is_return != 1 and customer in ({1})""".\
+				and grand_total > {0} and is_return != 1 and gst_category ='Unregistered' """.\
 					format(flt(b2c_limit), ", ".join([frappe.db.escape(c.name) for c in customers]))
 		elif self.filters.get("type_of_business") ==  "B2C Small" and customers:
 			conditions += """ and (
 				SUBSTR(place_of_supply, 1, 2) = SUBSTR(company_gstin, 1, 2)
-					or grand_total <= {0}) and is_return != 1 and customer in ({1})""".\
+					or grand_total <= {0}) and is_return != 1 and gst_category ='Unregistered' """.\
 						format(flt(b2c_limit), ", ".join([frappe.db.escape(c.name) for c in customers]))
 
 		elif self.filters.get("type_of_business") ==  "CDNR":