I don't think you want to involve analytics here, it's not aimed at debugging. Use the Test tab in api manager for that.
given you are obviously using fairly sizeable payloads let me remind you that using payload logging in analytics will hugely increase your system requirements for analytics in both storage and memory. If we normally store 5kb per event and you instead need to log say 200kb with payloads then you can see that the resources needed could be 40 times greater.
The major impact is on the memory needed rather than storage.
Given your payloads are encrypted there is zero value in logging them to analytics.
Afraid I can't help with the decryption issue but use the Test tab and you should be able to get more information out of the gateway as to what's happening.
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Chris Dudley
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