After trying everything I have read online (deleting rolling cache, changing bandwidth etc.) the FlyingIron Spitfire that I bought from the market place just will not download. It gets to about 30mib and will start going backwards, then restart downloading before failing altogether.
To state the obvious, in case you had installed the Spitfire before: did you remove any previous files and folders relating to the Spitfire, with e.g. the File Explorer?
I am asking because there had been „decompression“ issues with other aircrafts (specifically with the T-45C Goshawk that I know of) during aircraft upgrades, and deleting existing folders mostly helped in those cases.
(Those „decompression“ issues should be fixed in the sim marketplace - but still worth a try).