Timeline
May 4th, 2020 - From Amazon Support:
[13:38 PST] Service is once again operating at normal capacity at 2020-05-04 01:02:57 pm PST.
[12:49 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 12:45:46 pm PST. We are currently investigating the issue.
[12:16 PST] Service is once again operating at normal capacity at 2020-05-04 11:31:31 am PST.
[11:53 PST] Service is once again operating at normal capacity at 2020-05-04 11:31:31 am.
[11:05 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[10:35 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[10:06 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[09:35 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[09:05 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[08:35 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.
[08:05 PST] Service is reported to be experiencing slightly higher error rate starting at 2020-05-04 07:50:11 am PST. We are currently investigating the issue.

Issue
Amazon is reporting "Internal Error -" while shipping using Amazon Buy Shipping in SKULabs. You may also experience delays while fetching rates, missing rates from Amazon Buy Shipping, or other issues related to shipping and rating from Amazon.

Cause
This appears to be service-related troubles at Amazon for their Merchant Fulfillment services (Amazon Buy Shipping), but we're monitoring closely. You can check the MWS health dashboard to see if they've begun monitoring the situation.

What should I do?
Our first recommendation would be to disable your Amazon buy shipping carrier temporarily. You only need Amazon Buy Shipping for "Seller-Fulfilled Prime" but you may have other reasons to use Amazon Buy Shipping due to the benefits Amazon provides when purchasing their labels.

Otherwise, our second best suggestion is to wait a few seconds and then try to click the rates button once again. Once you have a rate visible, it should be selected in the rates pop-up to prevent a second request from being required when a label is generated.

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