Unable to Authenticate API User in CA1 Environment (500 INTERNAL_SERVER_ERROR on /authentication/credentials)

Dear all,

I am working on integrating Nintex AssureSign with Power Apps with a flow in the CA1 environment and have run into a persistent authentication issue.

Environment / Setup

• Environment: https://ca1.assuresign.net

• API endpoint: POST /api/documentnow/v3.7/authentication/credentials

• Account Context: acb8d12c-3389-447e-a6b8-620cf18f9e5c

• API User created in account.assuresign.net, scoped to Specific Environment → https://ca1.assuresign.net/

• API Key active, not expired

• CA1 Settings → DocumentNOW® Integration → Default File Retrieval Credential set to the same API user

What I’ve Tried

• Body variations:

  { "username": "don.wang@elections.ca_Lqq4s0Ue", "key": "************", "sessionLength": 60 }

• Added accountContext in body (and also tested removing it)

• Added header:

  x-assuresign-account-context: acb8d12c-3389-447e-a6b8-620cf18f9e5c

• Headers:

  Content-Type: application/json Accept: application/json

• Tested with Power Automate HTTP action and PowerShell (Invoke-RestMethod).

The Problem

Every request consistently returns:

{ "errorCode": "INTERNAL_SERVER_ERROR", "summary": "An Unknown Error Occurred. (Error code: LRP8V)" }

I’ve also seen 404s when the endpoint path was wrong, but with the correct /authentication/credentials path I only get 500 errors.

• Status Code: 500

• x-ms-service-request-id and x-ms-correlation-id are present in headers (happy to share with support if needed).

Question

Has anyone successfully authenticated an API User against CA1 recently?

• Is there a required difference in how API users must be created/scoped for CA1?

• Should the accountContext always be in the header vs. the body?

• Is there anything else on the CA1 tenant that must be enabled (e.g., roles/permissions for API user)?

Any guidance or confirmation from others using CA1 would be greatly appreciated.

Thanks in advance,
Don