atlantafawkes

For future people – this was an issue with W3 total cache (W3TC) database caching. Printful relies on the woocommerce rest API to manage products in WordPress and the database cache causes issues with queries/data used in the API. I needed to configure W3TC to not cache queries within the scope of the woocommerce rest API.

Short answer – you need to add the following in the “Never cache the following pages:” section in the database cache settings in W3TC (v1 and v2 are optional I think, I just put them in for good measure):
/wc/v3/*
/wc/v2/*
/wc/v1/*

Detailed answer – I noticed that Printful was uploading the first image and product information, but the featured image was not set and would stop progress from there. After speaking with support, I was notified they were receiving the following error from the woocommerce rest API: #3270 is an invalid image ID. and woocommerce_product_invalid_image_id

This gave me some clue. It appeared the API thought the uploaded image did not exist. I assumed this was occurring in the code to set the featured image – so I did some digging. It appeared other people were having this problem. My first thought was that the data was stale (or .. a race condition in the code) so I tried the first solution I dug up involving the error code and my caching plugin (W3TC): https://wordpress.org/support/topic/w3-total-cache-restapi-problem/page/2/

I was happy to find it fixed the issue.