You may have reached Shopify’s limit on the number of products/variants apps are able to create using API.
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Shopify introduced a limit in March 2019 on how many variants apps can create using the API. The limit is currently set to 1,000 variants per 24 hour period which means if you have 100 variants for 5 different products, it will be counted as 500 products
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When you have reached the limit, you will not be able to push any more products and will get a 429 error message that will look like this
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​Response code = 429. Response message = Too Many Requests
​ Product: Daily variant creation limit reached. Please try again later.
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You can ask Shopify to remove this limit on your store by contacting Shopify Support and asking them to increase your store limit but you will need to explain the reasons behind your request.