I've done this using PHP. I'm not sure of the details using B4A but it can be done:
Send the order file to a folder on the server, encrypted (if it contains credit card info) via FTP. I know B4A can do FTP so this can be done. On the server, create a cron job (that's a batch job on a Linux server) and have it run every 5 minutes or so looking for order files in that Order folder.
Write the cron script in what ever server-side scripting language you can code in, I'd do it in PHP. It's this script that does the inserts into the DB and anything else you want such as sending an email to you confirming the order is in the DB. Again, if you have credit card info you need to encrypt the number in the DB field table (I'm assuming you need to get and maintain PCI compliance for your merchant bank).
Another option, not a good one but an option, is to do your orders all by email but as I stated before, you cannot include any payment info in the emails so this might not work for you.