This is Ciara from the Content API support team. Thank you for reaching out.
It appears that there is no issue with the Content API as the value you submitted is shown correctly on the Raw Feed attributes: Content API. Moving forward, I understand that the value on the Final attributes does not match the value you submitted. Take note that the data shown on the Final attributes are the processed values for each attribute in your product data for this item, with attribute modifications made by supplemental feeds, automatic item updates, with feed rules applied, and after attribute rejection.
With that said, kindly check if you have setup any of the features mentioned above, and for further assistance, kindly reach out to the Merchant Center support as those features are no longer part of the Content API and they are the one primarily providing support for them.
Let me know if you have any questions.