Solution 1
Did you check Magento logs for errors? Also, check the browser console for any errors.
If you see any errors then post them in the reply so that someone can help you.
Solution 2
Open the URL and then open the console tab via inspect window or by ctrl + shift + I and then add the product to the cart.
Solution 3
Run the additional SQL lines below
UPDATE core_config_data
SET value = REPLACE(value, '<old root URL or domain>', '<new root URL or domain>')
WHERE path = 'design/head/includes';
Delete the cache with the command:
rm -rf var/cache/*
Hope this can help you! Let me know if you need further assistance.
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