Mobile Data troubleshooting
Some local mobile operators may not work out of the box. Here are some steps to take to fix this:
Enable data roaming
Example: NRJ Mobile in France
Despite NRJ mobile being a french operator, it relies on the Orange network, so the data roaming needs to be enabled.
Settings -> More -> Mobile Network -> Data roaming
After doing so, select the "real" operators:
Settings -> Sim management -> Roaming -> Data roaming -> Select Orange
Then verify that the correct APN is selected:
Settings -> Mobile Networks -> Access Point Names -> Select an existing one or create on if needed
Finally check that mobile data is enabled
Settings -> Data usage -> Mobile data