I recently needed to convert from SVG to DXF with PHP so i tried using the Inkscape commandline however this does not work.

Does anyone have a solution to either of these problems?

I never tried this before but my guess is that if the dxf is broken itself, you cannot convert it to svg from command line.

I have been looking online and it seems the DXF save is possibly done with a extension instead of being built in to the program? If so why is that and does it mean there is really no way to convert to DXF format with commandline? DXF export being broken could possibly be a bug with the commandline code also because it's fine doing it from the save menu.

Sorry I was misreading and was thinking of converting dxf to svg. Then my guess would be there are things in the svg that is not handled well by the export.
As dxf is a cad format, would filter effect, blurring, alpha channel, even gradients matter? Or layers and groups.
Some problems can be even with fonts and with line widths.
It is a try and error what can be exported to a good dxf and what not.

The actual DXF export works fine if you have Inkscape open and use "File > Save As" however when you use the command line it simply won't work at all. My current guess is you cannot convert to this format via the command line but i might be wrong.

I am not sure why it would not be available as a option though unless this is a bug since the DXF format is built into the program which just means the command line is probably incomplete even for Inkscape's default file formats. If this is the case hopefully it can be added to the command line options for a future version of the program.