Have an error stating "Your ManiaExchange account has not be linked with your ManiaPlanet account. Click here to link them.". However, when trying to link my accounts I get the following error:

Internal error
Something went wrong...

Error id: 00000000000000000000000000000000

Any help is appreciated.

I don't know why you're getting an error, but feel free to open a support ticket on the ManiaExchange Discord server and we can see about fixing it for you.