Magento does not support '/' in the Product SKU
There is a known bug in Magneto #8615 where some Magento API endpoints reject API calls for products with a '/' in the SKU.
This is a known issue in Magento:
https://github.com/magento/magento2/issues/8615
This causes Spark Shipping not to be able to make API calls for products with an '/' in the SKU.
Magento's recommendation to correct this issue is to remove the '/' from the SKU.