Getting error when using Oracle imp command to import dmp file
Basically, your first step should be to try specifying a larger buffer (one large enough to hold your LOB).  And, so you're not surprised, this operation can take many, many hours (or even days) depending on the size of the import.
And, IIRC, this error can also be thrown if your import version is less than your export version... so check that, if moar buffer doesn't fix this.
If that fails, you'll need to provide moar details.

ORA-22993: specified input amount is greater than actual source amount

*Cause:  (1) For LOB write, the amount of data received is different from the amount that was indicated would be sent.  (2) For LOB copy and loadfromfile, the end of the source LOB/FILE value was reached before the specified input amount was copied/loaded.
*Action: (1) will happen when using OCI's piecewise mechanism with polling or with a callback function.  Modify the code either to send the amount specified or to pass 0 as the input amount so that any amount of data can be sent.  (2) will happen if the specified input amount is too large for the source LOB/FILE given the starting source offset.  Either decrease the starting source offset, or decrease the amount to copy/load.