It may well be unsupported by this device. This can happen for a few reasons. If you are trying to save the data, I would then suggest putting it back in the original device and then either upload the data to a cloud or google account, or connect that device to a computer and move the files from the card to an empty folder on the computer.
Once that is done, then insert the card in the new device and format the card. If the phone will allow it. If not, then try a different card in the device and see if it has problems. If it does not, then you have a card that is either the wrong kind for the device you are using it in, or a card that is going bad. If it won't read any card, then the device needs repairing.
Should the phone allow the card to be formatted and work after this, then you can move the files back onto the card, while it is in the phone, so you can access them again.