The official way to report a bug is through the issue tracker on github (https://github.com/taborlab/FlowCal/issues). Try to be as explicit as possible when describing your issue. Ideally, a set of instructions to reproduce the error should be provided, together with the version of all the relevant packages you are using.
If you are interested in writing the code necessary to solve a bug, please visit How to Contribute</contribute/how_to> first.