Merchant validation error on Apple Pay payment processing

Hi, I'm developer in fintech company, we have setup process for onboarding merchants for our partner and processing payments with usage of Apple Pay API. Daily system is processing ca. 10k payments but every day ca. 100 of transactions are declined because of merchant validation error: request to https://apple-pay-gateway.apple.com/paymentservices/paymentSession (with all required parameters in body) is returning response with status code 417 "statusMessage": "Payment Services Exception merchantId={root merchant id} unauthorized to process transactions on behalf of merchantId={merchant id hash} reason={merchant id hash} is not a registered merchant in WWDR and isn't properly authorized via Mass Enablement, either." Issue impacts recurring merchants, most of their transactions are processed successfully but randomly some of them are failing with such reason. All prerequisites are met: merchant have deployed 'apple-developer-merchantid-domain-association' certificate, certificates are valid and not expired. Apple Support is not able to provide any information based on provided requests timestamps. We would to know what may be the reason just part of the requests are failing and what 417 error code means.

Merchant validation error on Apple Pay payment processing
 
 
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