ServiceNow Service Catalog Cart API error Exception While Reading Request

if you get this http status 500 error when attempting the Service Catalog API POST operation (for example, order_now)

com.glide.rest.domain.ServiceException: Exception while reading request

Consider what roles your user might need to authenticate (e.g. rest) and also setting this property to 'allow': glide.sc.req_for.roles.default

Consider adding these to the HTTP Headers of the REST Message:

Accept	application/json

application/json

Content-Type	application/json

application/json