maybe m3u is from different service, usually Mag portal and m3u have the same channel listing.

I use helix but my channels are the same on mag and m3u? What channel is missing/ additional on one or the other?

Differt channel groups or bouqets

Make sure that the portal isn't caching the channel list, and that your m3u is pulling from the server and isn't a local file.

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*EDIT* I also have Helix, and see the same on both m3u & portal.

Check your EPG offset in the settings. You might have your listings shifted by a number of hours for one of them.

If you have a subscription with a mac address you automatically have one with m3u link or it depend of the service provider?

helix has the ability to edit the mac bouquet separate from the line bouquet - although its same account.

It is NOT a common thing among suppliers actually most suppliers no logger offer linking mac to a line account for security reasons.