Most apps can't run off an SD card, which is "External" storage. They require it be set as "Internal" storage. Now this will only work if your device is running Android "Marshmallow" or newer and the manufacturer has not restricted that option on that device.
How to turn the "External" SD card into "Internal" storage on "Marshmallow".
NOTE: Please be sure you start with a blank SD card. It needs to be blank because when the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device).
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format...