So this is my first ever attempt at uploading a track on TMX and I couldn't do it. Next to the track section after trying to upload it says 'Specific method is not supported' I have no idea why.
I made the track in United Forever and I don't know if it's that or just the file type. I tried the the .challenge.gbx and retried simply by renaming it to .map.gbx
Any help would be greatly appreciated.

P.S. Never mind, I realised I didn't use the TMForever Exchange.

I'm glad you were able to figure it out.

For future reference, the track sharing sites are:

ManiaExchange (for TrackMania 2)
The site you're on now... for TM2 Canyon, TM2 Valley, TM2 Stadium, and soon TM2 Lagoon tracks.

ManiaExchange (for ShootMania)
The other subdomain at MX. For ShootMania map sharing.

TrackMania Exchange - United
Originally for TrackMania United tracks. Now for TrackMania United Forever tracks.

TrackMania Exchange - Nations Forever
For TrackMania Nations Forever tracks, or Stadium tracks built in TrackMania United Forever.

TrackMania Exchange - Nations
For tracks built in the original version of Stadium, TrackMania Nations ESWC.

TrackMania Exchange - Sunrise
For Bay, Coast, and Island tracks built in TrackMania Sunrise and its expansions.

TrackMania Exchange - Original
For Desert (American?), Rally (Countryside), and Snow (Alpine) tracks built in the original TrackMania.

The above sites were created by and are run by volunteers. Basically, they're Fan Sites.

There is also the sharing sites for TrackMania Turbo tracks:
PC | XBOX ONE | PS4

But those are run by Ubisoft.

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Generally tracks from Original, Sunrise, Nations, Nations Forever, and United.... can all be played in United Forever, which is pretty cool!

And Stadium tracks from Nations, Nations Forever, United, and United Forever can be pretty easily converted for use in TM2 Stadium.

I guess I should mention that some people also use Steam Workshop for sharing some TM2 and ShootMania maps. But, since I don't play TM2 via Steam, I don't know much about it.

I think steam is full of "My first map" kinda maps
nothing actually looks worth playing tbh

To be honest, that's probably because everyone who starts making maps with any quality migrates over here. The Steam Workshop system isn't bad per se, it's just that Mania Exchange's system is just better in every aspect with the possible exception of ease of use. Some people (myself included) put their maps on both places.

I am trying to upload another one of my tracks, never had this problem before or received this message. What does this mean? Property accessor 'IsMP4' on object 'TmExchange.Core.Models.TrackInfo' threw the following exception:'Object reference not set to an instance of an object.'

Should be fixed now, sorry!

Thank you so much. It uploaded perfectly as normal. I was panicking because we have over 200 hours of work and MT work with this track and was afraid there was something wrong with the track. You made my day bud. Thank you again, Red Virus