All I know is that the WooCommerce/Printful integration doesn’t work here. Maybe there are competitors to Printful which do work here, or maybe other platforms which integrate with Printful in a way which does work here.
Feel free to try to make it work, but don’t be too surprise if you won’t be able to.
Are you using one of our free SSL certificates by any chance? Since free hosting doesn’t support uploading CA chains, automated systems may get SSL errors like this.
You could try to enable Cloudflare on your website instead (using Cloudflare’s nameservers is recommended for this). Cloudflare’s SSL system works differently and may not have this issue.
If you are going to use Cloudflare with WordPress, please do make sure that both are configured correctly to work together: