WooCommerce Require Category Minimum for Purchase

wc-require-cat-minimum.php

<?php
/**
 * only copy the opening php tag if needed
 * tutorial at: http://swwp.co/6l
 */
 
/**
 * Renders notices and prevents checkout if the cart
 * does not contain a minimum number of products in a category
 */
function sww_check_category_for_minimum() {

	// set the minimum quantity in the category to purchase
	$min_quantity = 6;

	// set the id of the category for which we're requiring a minimum quantity
	$category_id = 15;

	// get the product category
	$product_cat = get_term( $category_id, 'product_cat' );
	$category_name = '<a href="' . get_term_link( $category_id, 'product_cat' ) . '">' . $product_cat->name . '</a>';

	// get the quantity category in the cart
	$category_quantity = sww_get_category_quantity_in_cart( $category_id );

	if ( $category_quantity < $min_quantity ) {
		// render a notice to explain the minimum
		wc_add_notice( sprintf( 'Sorry, you must purchase at least %1$s products from the %2$s category to check out.', $min_quantity, $category_name ), 'error' );
	}

}
add_action( 'woocommerce_check_cart_items', 'sww_check_category_for_minimum' );


/**
 * Returns the quantity of products from a given category in the WC cart
 * 
 * @param int $category_id the ID of the product category
 * @return in $category_quantity the quantity of products in the cart belonging to this category
 */
function sww_get_category_quantity_in_cart( $category_id ) {

	// get the quantities of cart items to check against
	$quantities = WC()->cart->get_cart_item_quantities();
	
	// start a counter for the quantity of items from this category
	$category_quantity = 0;

	// loop through cart items to check the product categories
	foreach ( $quantities as $product_id => $quantity ) {

		$product_categories = get_the_terms( $product_id, 'product_cat' );
		
		// check the categories for our desired one
		foreach ( $product_categories as $category ) {

			// if we find it, add the line item quantity to the category total
			if ( $category_id === $category->term_id ) {
				$category_quantity += $quantity;
			}
		}
	}

	return $category_quantity;
}

Thank you for that!
I have a question:
I want to do that on my E-commerce site. I have a lot of categories and I want that just in this one category it will require 4 units min (lets call it "66").
When I put this code its require to buy at least 4 units from a category "66". even when someone wants to buy from a different category it is required to buy from category "66".

Can you help me please?
Thanks

@bekarice thank you for solution!

function sww_check_category_for_minimum() {

// set the minimum quantity in the category to purchase
$min_quantity = 3;

// set the id of the category for which we're requiring a minimum quantity
$category_id = 89;

// get the product category
$product_cat = get_term( $category_id, 'product_cat' );
$category_name = '<a href="' . get_term_link( $category_id, 'product_cat' ) . '">' . $product_cat->name . '</a>';

// get the quantity category in the cart
$category_quantity = sww_get_category_quantity_in_cart( $category_id );

if ( $category_quantity < $min_quantity ) {
	// render a notice to explain the minimum
	wc_add_notice( sprintf( 'Sorry, you must purchase at least %1$s products from the %2$s category to check out.', $min_quantity, $category_name ), 'error' );
}

}
add_action( 'woocommerce_check_cart_items', 'sww_check_category_for_minimum' );

/**

• Returns the quantity of products from a given category in the WC cart

• @param int $category_id the ID of the product category

• @return in $category_quantity the quantity of products in the cart belonging to this category
  */
  function sww_get_category_quantity_in_cart( $category_id ) {

  // get the quantities of cart items to check against
  $quantities = WC()->cart->get_cart_item_quantities();

  // start a counter for the quantity of items from this category
  $category_quantity = 0;

  // loop through cart items to check the product categories
  foreach ( $quantities as $product_id => $quantity ) {

   $product_categories = get_the_terms( $product_id, 'product_cat' );
   
   // check the categories for our desired one
   foreach ( $product_categories as $category ) {
  
   	// if we find it, add the line item quantity to the category total
   	if ( $category_id === $category->term_id ) {
   		$category_quantity += $quantity;
   	}
   }
  

  }

  return $category_quantity;
  }

I have added this to function.php.
If I have less than 3 products from green grocery (category id- 89) it shows an error but let's say I don't want to buy 3rd item, instead I remove two items from green grocery category but when I remove that category products, the error still stays there - https://prnt.sc/115nxlu
How do I resolve tyis ?