Magento 2 : The requested qty is not available

Question

While applying shipping using "/V1/stripe/payments/apply_shipping" api call, if the product's (simple product of config) product qty is 1 exact then it falls into below condition in file.

Magento2/vendor/magento/module-catalog-inventory/Model/StockStateProvider.php

if (!$this->checkQty($stockItem, $summaryQty) || !$this->checkQty($stockItem, $qty)) {
            
            $message = __('The requested qty is not available');

I am not sure why its happening, any thoughts on this ?