To extend internal storage on SD card, you have to format the SD card with 2 patitions, one in FAT32 or extFAT, and the second in ext4 (if Android 5 or later). And then use Link2SD.

You can create partitions use a PC with “MiniTool Partition Wizard” to make second partition of “ext4” file format on SD-Card for use with Link2SD and Internal Memory Scripts.

Format the first partition as “Primary” with fat32, and a second partition as “Primary” again, select file system “ext4” and give label name as “sd-ext”

Then put the SDcard in the phone and use Link2SD with the “Mount script” to extend you internal storage.