using api Billing Integration SAP_COM_0120 problem

Dear Expert,

we are developing fiori app deploy in sap cloud platform, and need to create a billing from dn in s4 hana cloud,

we find the api SAP_COM_0120, but this api only contain read and cancel method in odata service, the api only support create billing in soap service and rfc service.

we test the soap service in soap ui but get an error response， the test xml data we used like this billing document creation.txt,

the response data is following

<soap-env:Envelope xmlns:soap-env="http://schemas.xmlsoap.org/soap/envelope/">
<soap-env:Header/>
<soap-env:Body>
<soap-env:Fault>
<faultcode>soap-env:Server</faultcode>
<faultstring xml:lang="en">Web service processing error; more details in the web service error log on provider side (UTC timestamp 20190613132758; Transaction ID 968F5D42D8BB0250E005CFC0666EADDF) The error log can be accessed by service provider from SAP backend</faultstring>
<detail/>
</soap-env:Fault>
</soap-env:Body>
</soap-env:Envelope>

how can we solve this problem? and is there any way to analyze it ?

if we can't solve this problem, how can we use rfc method on sap cloud by ui5?

many thanks!