When  installing the 757, use Manual Offline Activation and select GENERATE AND SEND YOUR  SYSTEM CODE
A code_y572.txt (for the 757 Captain III Base Pack (P3D4/5))  is created and you need to save this file on your PC
Copy it to your android phone.
Navigate to this address - https://www.captainsim.com/activ/offline.php - and browse for, and upload the code_y572.txt and select Get a Key
After you request a key, a file named key_y572.txt is created, and you need to save it to your android phone
Copy the key_y572.txt back to your PC, and when you install the 757, select USE A KEY RECIEVED FROM CAPTAIN SIM  - use the key_y572.txt to unlock the 757




Note. For FSX/SE/P3D3, the text files are code_x572.txt, and key_x572.txt