This is a known limitation with Big Commerce and the Safari Browser. Make a quick setting change and this should be working after that.
The Problem: You aren't able to login to Spark from within Big Commerce while you are using the Safari browser.
- In Safari, click on the Safari menu; then click Preferences
- Click Privacy
- In Website Tracking: Prevent cross-site tracking, uncheck the checkbox and close the window
- Now go back to Big Commerce and click on My Apps and then Spark Shipping
- You should now be able to login successfully
If you have any other issues, contact us at firstname.lastname@example.org