ORA-1654: unable to extend index HR.PAY_RUN_RESULT_VALUES_PK by 8195 in tablespace HRX

There is 40GB of free space available in that Tablespace.

I think the index couldnot able to find the contiguous space of 8195.I coalesecd the Tbalespace even after that the same error is popping up.

Temporarly to resolve the issue we had to increase the tablespace by adding a datafile '/mnt/oraprod/proddata/fs04/hrx18.dbf' of size 2000M.

Is there any other solution to avoid this issue please??