ORA-65342: source pluggable database has unrecovered transaction

Starting 12.2, if you are planning to clone a PDB locally or remotely, you can do that while source PDB is open in read-write mode (hot cloning). In 12.1, if you start your CREATE PLUGGABLE DATABASE command while a transaction is already active in the source PB, you will be returned ORA-65342. Therefore, the better option is to close the source PDB, and then start it as read-only so that no transactions could hinder the cloning process

SQL> create pluggable database MYPDB from PRODPDB; create pluggable database MYPDB from PRODPDB * ERROR at line 1: ORA-65342: source pluggable database PRODPDB has unrecovered transaction