On your 1st device (source)

(1) Make sure to link your dropbox account to Invoice King. Please refer to this link for the guide.

(2) Then create a backup. Please refer to this link for the guide.

Then from your 2nd device (destination):

(1) Link your dropbox account to Invoice King.

(2) Then restore the newly created backup. Choose the topmost file to restore the lastest backup. Please to refer to this link for the guide.