I'm seeing xa_start failures , when we are trying insert  a message to a database.  Trying to explain the scenario in-detail.

We are running on AIX 7.1 machine

1. Push a message to MQ [version 9.0.0.0] queue

2. In IIB [IIB version- 10.0.0.9] , a Message flow picks up message from MQ queue and inserts message to oracle database [ oracle version- 12.1.0.2.0] 

3. Using XA global transaction at flow level.

In above scenario, message is failing at 2nd step with the error :

 '-1' '[IBM][ODBC Oracle Wire Protocol driver]xa_start() failed.' 'HY000'.

BIP8270I: Connected to Datasource 'XXXX' as user 'XXXX'. The datasource platform is 'Oracle', version '12.01.0000 Oracle 12.1.0.2.0'.
===========================
databaseProviderVersion = 12.01.0000 Oracle 12.1.0.2.0
driverVersion = 07.16.0292 (B0337, U0221)
driverOdbcVersion = 03.52
driverManagerVersion = 03.52.0002.0002
driverManagerOdbcVersion = 03.52
databaseProviderName = Oracle

Followed all the steps suggested as per IBM and oracle for XA setup. 

can someone help me on troubleshooting/resolving  the issue.

IIB-10.0.0.9 doesn't have separate installation for DatabaseExtender. All  ODBC drivers come along with the IIB.