allowShrinking

Explicitly tells the wallet that it is allowed to reduce the amount of the output matching this scriptPubKey in order to bump the transaction fee. Without specifying this the wallet will attempt to find a change output to shrink instead. Note that the output may shrink to below the dust limit and therefore be removed. If it is preserved then it is currently not guaranteed to be in the same position as it was originally. Returns an error if scriptPubkey can’t be found among the recipients of the transaction we are bumping.