WHMCS prepaid module 500 internal server error SolusVM2

Symptoms 

SolusVM 2 VPS creation via WHMCS prepaid module fails with the following error:

SVM_ERROR: https://example.com/api/v1/users` resulted in a `500 Internal Server Error` response: { "message": "Server Error" } "

Cause

SolusVM 2 bug with ID #SIO-4712 which was fixed in SolusVM 2 version 2.0.0-27449

Resolution

Update SolusVM 2 to the latest mainline version.