Cause:

29335, 00000, "tablespace '%s' is not read only"
// *Cause: The tablespace is not read only.
// *Action: Make the tablespace read only and retry the operation.

Transportable tablespace got failed during export due to read write tablespaces

Solution:

Check the tablespace for self containment without dependent data

SQL> exec dbms_tts.transport_set_check('EXAMPLE',true);

PL/SQL procedure successfully completed.

Make the tablespace readonly to maintain consistency of data

SQL> exec dbms_tts.transport_set_check('EXAMPLE',true);

PL/SQL procedure successfully completed.

Start the export

Starting "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01":  system/******** parfile=ttbs.par
Processing object type TRANSPORTABLE_EXPORT/PLUGTS_BLK
Processing object type TRANSPORTABLE_EXPORT/STATISTICS/MARKER
Processing object type TRANSPORTABLE_EXPORT/POST_INSTANCE/PLUGTS_BLK
Master table "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_TRANSPORTABLE_01 is:
  /tmp/ttbs.dmp
******************************************************************************
Datafiles required for transportable tablespace EXAMPLE:
  /app01/EXAMPLE12625.dbf
  /app01/EXAMPLE6345.dbf
  /app01/EXAMPLE7187.dbf
  /app01/oracle/product/base/oradata/orcl12x/example01.dbf
Job "SYSTEM"."SYS_EXPORT_TRANSPORTABLE_01" successfully completed at Wed Jan 13 16:22:24 2021 elapsed 0 00:00:14

Export is successful !