i had faced the same issue few days back. it is a behavior in 8.2 which got introduced in one of the fix to support WSDL generated in earlier versions.
check your field for which you are getting error. you have set namspace key but no value or vice versa. so either clean it up and then generate or complete the key value pair.
few other option you can try if you are not in position to edit document
watt.server.soap.decodeElementWithPrefix=true - set in extended setting and restart IS. this may work depending if you created this service in earlier version vs if it is a new one. i guess yours is a newly created in 8.2. this setting didn’t work for me.
Let me know if this work for you.
My suggestion will be to clean up your documents to have a proper key/value pair of namespace as this is a new implementation and you will save yourself from future issues.
#API-Management#webMethods#soa