If you are unable to see quantity incrementor on the Checkout page, then there could be two possibilities due to which quantity selector is not visible on your Checkout page.
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Here we will discuss both possibilities one by one to check why Quantity Selector is not visible.
Possibility 1: Hidden using Product Inventory Settings
If the product is set to be sold individually through product inventory, Quantity Selector will not be visible on the Checkout page.
Step 1: Suppose you have a product “Simple D3 Supplement 6768” in your cart for which the Quantity Selector is not visible.
Edit this product by going to WooCommerce > Products.
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Step 2: Here click on the "Inventory" tab.
Untick the option labeled as "Enable this to only allow one of this item to be bought in a single order" if ticked.
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Step 3: Click on the "Update" button to save changes.
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Final Output:
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Possibility 2: Hide from product field on Checkout page
Step 1: Select a Checkout page > Go to the 'Fields' tab and then click on the 'Products' field.
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Step 2: Click on the “Advanced” tab and untick the checkbox labeled “Hide Product Incrementor” to show the product incrementor.
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Once done, click on Update.
Step 3: Hit the “Save changes” button to publish the changes
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Final Output:
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This is how you can enable the product quantity incrementor on the Checkout page.