Unsuccessful Merchants Services Payments API Calls

Hi,

Please help with the following issue: I'm unable to successfully call the Disbursement transactions API endpoint any other endpoints of the Payments API. I'm able to successfully call desired endpoints of the Raiser's Edge NXT API endpoints however. I've ensured I have the correct role assignments - the Merchant Services and Payments API roles. Please see below :

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I've also ensured that in my application I have full data access (see below):

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I'm generating the access token using POSTMAN. When I use this access token the Payments API call is unsuccessful. When I however replace this access token using the Raiser's Edge generated access token (see below) then the Payments API call is successful

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I'm out of ideas about what the issue is, so help would definitely be very appreciated.