Fix checkout fatal when a cart line price is not numeric

changelog.txt

@@ -1,5 +1,8 @@
 *** WooCommerce Tax Changelog ***
 
+= 3.6.14 - 2026-xx-xx =
+* Fix   - Prevent a fatal error at checkout when a cart line's price is not numeric.
+
 = 3.6.13 - 2026-08-24 =
 * Tweak - WordPress 7.1 Compatibility.
 

classes/class-wc-connect-taxjar-integration.php

@@ -1055,14 +1055,17 @@ protected function get_line_items( $wc_cart_object ) {
 				$this->_log( 'Tax location override for product ' . $id . ': ' . $default_location . ' -> ' . $tax_location );
 			}
 
-			$line_items[ $cart_item_key ] = array(
-				'id'               => $id,
-				'quantity'         => $quantity,
-				'product_tax_code' => $tax_code,
-				'unit_price'       => $unit_price,
-				'discount'         => $discount,
-				'tax_location'     => $tax_location,
-			);
+			// A malformed price reduces to '' or '-', which is fatal in the totals arithmetic. A 0 is legitimate.
+			if ( is_numeric( $unit_price ) ) {
+				$line_items[ $cart_item_key ] = array(
+					'id'               => $id,
+					'quantity'         => $quantity,
+					'product_tax_code' => $tax_code,
+					'unit_price'       => $unit_price,
+					'discount'         => $discount,
+					'tax_location'     => $tax_location,
+				);
+			}
 		}
 
 		// Re-keys $non_taxable_line_items onto the canonical ids as it goes.

readme.txt

@@ -70,6 +70,9 @@ This plugin relies on the following external services:
 
 == Changelog ==
 
+= 3.6.14 - 2026-xx-xx =
+* Fix   - Prevent a fatal error at checkout when a cart line's price is not numeric.
+
 = 3.6.13 - 2026-08-24 =
 * Tweak - WordPress 7.1 Compatibility.
 

tests/php/test-class-wc-connect-taxjar-integration.php

@@ -87,6 +87,7 @@ public function tear_down() {
 		remove_all_filters( 'woocommerce_tax_line_item_location' );
 		remove_all_filters( 'woocommerce_services_override_tax_rate' );
 		remove_all_filters( 'woocommerce_product_is_taxable' );
+		remove_all_filters( 'woocommerce_product_get_price' );
 
 		delete_option( 'woocommerce_calc_taxes' );
 
@@ -445,6 +446,44 @@ public function test_get_line_items_structure() {
 		$this->assertEquals( 2, $item['quantity'] );
 	}
 
+	/**
+	 * A pricing filter can empty a price after the item is already in the cart.
+	 * wc_format_decimal() passes that through, and a non-numeric unit price is fatal
+	 * in the totals arithmetic, so the line is skipped.
+	 */
+	public function test_get_line_items_skips_line_with_non_numeric_price() {
+		$this->product = WC_Helper_Product::create_simple_product();
+		$this->product->save();
+
+		WC()->cart->add_to_cart( $this->product->get_id(), 2 );
+
+		add_filter( 'woocommerce_product_get_price', '__return_empty_string' );
+		$line_items = $this->invoke_protected_method( 'get_line_items', array( WC()->cart ) );
+		remove_filter( 'woocommerce_product_get_price', '__return_empty_string' );
+
+		$this->assertSame( array(), $line_items );
+	}
+
+	/**
+	 * A zero price is legitimate and must keep reaching TaxJar, so the guard has to be
+	 * is_numeric() and not a truthiness check. See
+	 * test_zero_amount_response_persists_real_itemized_rates() for what the response to
+	 * a $0 line carries.
+	 */
+	public function test_get_line_items_keeps_line_priced_zero() {
+		$this->product = WC_Helper_Product::create_simple_product();
+		$this->product->set_regular_price( 0 );
+		$this->product->set_price( 0 );
+		$this->product->save();
+
+		WC()->cart->add_to_cart( $this->product->get_id(), 2 );
+
+		$line_items = $this->invoke_protected_method( 'get_line_items', array( WC()->cart ) );
+
+		$this->assertCount( 1, $line_items );
+		$this->assertSame( '0', reset( $line_items )['unit_price'] );
+	}
+
 	// -------------------------------------------------------------------------
 	// group_items_by_location() tests
 	// -------------------------------------------------------------------------