This is the params as they are sending it back, and as Rails interprets it.

Params Expressed as XML

2017-07-12T02:10:27.590246+00:00 app[web.1]: 
params

{"------"=>"_Part_5933_1106131660.1499825426832\r\nMIME-Version: 1.0\r\nContent-Type: multipart/related", "\r\n\tboundary"=>"\"----=_Part_5902_1862233434.1499825426375\"", "\r\n\ttype"=>"\"application/xml\"\r\nContent-ID: <VPGKFYLCEJLNKPZJIWWC-1499825426372-DFIIUUZTQB>\r\nContent-Description: This is the RosettaNet Business Message\r\n\r\n------=_Part_5902_1862233434.1499825426375\r\nContent-Type: Application/XML\r\nContent-Transfer-Encoding: binary\r\nContent-Location: RN-Preamble\r\nContent-ID: <PreambleHeader.0.3408657695604992.1499825426373@p2plouiex>\r\n\r\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<!DOCTYPE Preamble SYSTEM \"Preamble_MS_V02_00.dtd\">\r\n<Preamble>\r\n<standardName>\r\n<GlobalAdministeringAuthorityCode>RosettaNet</GlobalAdministeringAuthorityCode>\r\n</standardName>\r\n<standardVersion>\r\n<VersionIdentifier>V02.00</VersionIdentifier>\r\n</standardVersion>\r\n</Preamble>\r\n\r\n------=_Part_5902_1862233434.1499825426375\r\nContent-Type: Application/XML\r\nContent-Transfer-Encoding: binary\r\nContent-Location: RN-Delivery-Header\r\nContent-ID: <DeliveryHeader.0.3408657695604992.1499825426373@p2plouiex>\r\n\r\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<!DOCTYPE DeliveryHeader SYSTEM \"DeliveryHeader_MS_V02_00.dtd\">\r\n<DeliveryHeader>\r\n<isSecureTransportRequired>\r\n<AffirmationIndicator>Yes</AffirmationIndicator>\r\n</isSecureTransportRequired>\r\n<messageDateTime>\r\n<DateTimeStamp>20170712T021026.374Z</DateTimeStamp>\r\n</messageDateTime>\r\n<messageReceiverIdentification>\r\n<PartnerIdentification>\r\n<domain>\r\n<FreeFormText>DUNS</FreeFormText>\r\n</domain>\r\n<GlobalBusinessIdentifier></GlobalBusinessIdentifier>\r\n</PartnerIdentification>\r\n</messageReceiverIdentification>\r\n<messageSenderIdentification>\r\n<PartnerIdentification>\r\n<domain>\r\n<FreeFormText>DUNS</FreeFormText>\r\n</domain>\r\n<GlobalBusinessIdentifier></GlobalBusinessIdentifier>\r\n</PartnerIdentification>\r\n</messageSenderIdentification>\r\n<messageTrackingID>\r\n<InstanceIdentifier>ac1aabd9000048fd0000005b1499825426437</InstanceIdentifier>\r\n</messageTrackingID>\r\n</DeliveryHeader>\r\n\r\n------=_Part_5902_1862233434.1499825426375\r\nContent-Type: Application/XML\r\nContent-Transfer-Encoding: binary\r\nContent-Location: RN-Service-Header\r\nContent-ID: <ServiceHeader.0.3411345148771141.1499825426374@p2plouiex>\r\nContent-Description: RosettaNet-Service-Header\r\n\r\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<!DOCTYPE ServiceHeader SYSTEM \"ServiceHeader_MS_V02_00.dtd\">\r\n<ServiceHeader>\r\n<ProcessControl>\r\n<ActivityControl>\r\n<BusinessActivityIdentifier>Invoice</BusinessActivityIdentifier>\r\n<MessageControl>\r\n<fromRole>\r\n<GlobalPartnerRoleClassificationCode>Buyer</GlobalPartnerRoleClassificationCode>\r\n</fromRole>\r\n<fromService>\r\n<GlobalBusinessServiceCode>Buyer Service</GlobalBusinessServiceCode>\r\n</fromService>\r\n<inReplyTo>\r\n<ActionControl>\r\n<ActionIdentity>\r\n<GlobalBusinessActionCode>Invoice Notification</GlobalBusinessActionCode>\r\n<messageStandard>\r\n<FreeFormText>PIDX</FreeFormText>\r\n</messageStandard>\r\n<standardVersion>\r\n<VersionIdentifier>1.0</VersionIdentifier>\r\n</standardVersion>\r\n</ActionIdentity>\r\n<messageTrackingID>\r\n<InstanceIdentifier>7B8FB4781849AAB8C8ECBEA488FF5BF7</InstanceIdentifier>\r\n</messageTrackingID>\r\n</ActionControl>\r\n</inReplyTo>\r\n<Manifest>\r\n<numberOfAttachments>\r\n<CountableAmount>0</CountableAmount>\r\n</numberOfAttachments>\r\n<ServiceContentControl>\r\n<SignalIdentity>\r\n<GlobalBusinessSignalCode>Exception</GlobalBusinessSignalCode>\r\n<VersionIdentifier>V02.00</VersionIdentifier>\r\n</SignalIdentity>\r\n</ServiceContentControl>\r\n</Manifest>\r\n<toRole>\r\n<GlobalPartnerRoleClassificationCode>Seller</GlobalPartnerRoleClassificationCode>\r\n</toRole>\r\n<toService>\r\n<GlobalBusinessServiceCode>Seller Service</GlobalBusinessServiceCode>\r\n</toService>\r\n</MessageControl>\r\n</ActivityControl>\r\n<GlobalUsageCode>Test</GlobalUsageCode>\r\n<partnerDefinedPIPPayloadBindingId>\r\n<ProprietaryReferenceIdentifier>PIDX</ProprietaryReferenceIdentifier>\r\n</partnerDefinedPIPPayloadBindingId>\r\n<pipCode>\r\n<GlobalProcessIndicatorCode>P21</GlobalProcessIndicatorCode>\r\n</pipCode>\r\n<pipInstanceId>\r\n<InstanceIdentifier>7B8FB4781849AAB8C8ECBEA488FF5BF7</InstanceIdentifier>\r\n</pipInstanceId>\r\n<pipVersion>\r\n<VersionIdentifier>1.0</VersionIdentifier>\r\n</pipVersion>\r\n<KnownInitiatingPartner>\r\n<PartnerIdentification>\r\n<domain>\r\n<FreeFormText>DUNS</FreeFormText>\r\n</domain>\r\n<GlobalBusinessIdentifier></GlobalBusinessIdentifier>\r\n<locationID>\r\n<Value></Value>\r\n</locationID>\r\n</PartnerIdentification>\r\n</KnownInitiatingPartner>\r\n</ProcessControl>\r\n</ServiceHeader>\r\n\r\n------=_Part_5902_1862233434.1499825426375\r\nContent-Type: Application/XML\r\nContent-Transfer-Encoding: binary\r\nContent-Location: RN-Service-Content\r\nContent-ID: <ServiceContent.0.3411345148771141.1499825426374@p2plouiex>\r\nContent-Description: RosettaNet-Service-Content\r\n\r\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\r\n<!DOCTYPE Exception SYSTEM \"Exception_MS_V02_00.dtd\">\r\n<Exception>\r\n<ExceptionDescription>\r\n<errorClassification>\r\n<GlobalMessageExceptionCode>PRF.ACTN.GENERR</GlobalMessageExceptionCode>\r\n</errorClassification>\r\n<errorDescription>\r\n<FreeFormText>Errors: The Invoice Number entered already exists.</FreeFormText>\r\n</errorDescription>\r\n<offendingMessageComponent>\r\n<GlobalMessageComponentCode>ServiceContent</GlobalMessageComponentCode>\r\n</offendingMessageComponent>\r\n</ExceptionDescription>\r\n<GlobalExceptionTypeCode>General Exception</GlobalExceptionTypeCode>\r\n</Exception>\r\n\r\n------=_Part_5902_1862233434.1499825426375--\r\n\r\n------=_Part_5933_1106131660.1499825426832--\r\n", "controller"=>"api", "action"=>"open_invoice_return"}

If you click Raw you can see it better.