Unable to send an inreach SMS to numbers of the FREE operator

In some cases, this is because of the shortened URL in the SMS message - the one that sends you to a map page showing the location. Sometimes, turning this off helps. You can do that at explore.garmin.com, in the lower right corner of the Account tab.

If that doesn't help, you might try opening a support ticket with your local support organization. Sometimes Garmin will intervene to convince a provider to pass their short URLs (or whatever else is causes the provider to block messages).

hello, the pre-written message was sent simultaneously to several correspondents, only those with a FREE line do not receive it, those with ORANGE or BOUYGUE lines receive it correctly during the same sending. I tried not to send the map, it does not change the problem. A ticket has already been opened with GARMIN FRANCE.
It appears from all my attempts and tests that FREE blocks the INREACH number because it is not identifiable.

Not sure if this is what you mean by "identifiable", but - Garmin uses a (more or less) local SMS gateway to send SMS to cell phones. Gateway varies according to the "location" of the recipient's cell number. The gateway selects the number "from which" the message appears to originate. The equivalent of "caller ID" (if any) will come back to the gateway, not to Garmin.

sorry, I'm French, "unidentifiable" means that the sender's phone number cannot be verified by FREE, 
because it is virtual and does not belong to any real subscriber.

After opening a ticket to Garmin support, the problem is resolved since yesterday, but I have not received an explanation.

many thanks