fix: basic validations for Membership Type Linked Item
diff --git a/erpnext/non_profit/doctype/membership_type/membership_type.js b/erpnext/non_profit/doctype/membership_type/membership_type.js
index 94ccdd8..5bd8a6c 100644
--- a/erpnext/non_profit/doctype/membership_type/membership_type.js
+++ b/erpnext/non_profit/doctype/membership_type/membership_type.js
@@ -3,12 +3,20 @@
 
 frappe.ui.form.on('Membership Type', {
 	refresh: function (frm) {
-		frappe.db.get_single_value("Membership Settings", "enable_razorpay").then(val => {
+		frappe.db.get_single_value('Membership Settings', 'enable_razorpay').then(val => {
 			if (val) frm.set_df_property('razorpay_plan_id', 'hidden', false);
 		});
 
-		frappe.db.get_single_value("Membership Settings", "enable_invoicing").then(val => {
+		frappe.db.get_single_value('Membership Settings', 'enable_invoicing').then(val => {
 			if (val) frm.set_df_property('linked_item', 'hidden', false);
 		});
+
+		frm.set_query('linked_item', () => {
+			return {
+				filters: {
+					is_stock_item: 0
+				}
+			}
+		})
 	}
 });
diff --git a/erpnext/non_profit/doctype/membership_type/membership_type.py b/erpnext/non_profit/doctype/membership_type/membership_type.py
index b95b043..38e6f65 100644
--- a/erpnext/non_profit/doctype/membership_type/membership_type.py
+++ b/erpnext/non_profit/doctype/membership_type/membership_type.py
@@ -7,7 +7,11 @@
 import frappe
 
 class MembershipType(Document):
-	pass
+	def validate(self):
+		if self.linked_item:
+			is_stock_item = frappe.db.get_value("Item", self.linked_item, "is_stock_item")
+			if is_stock_item:
+				frappe.throw(_("The Linked Item should be a service item"))
 
 def get_membership_type(razorpay_id):
 	return frappe.db.exists("Membership Type", {"razorpay_plan_id": razorpay_id})
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