The FDCPA only offers protection to consumers for private debts. Here is the specific wording from the FDCPA:
” Any obligation or alleged obligation of a consumer to pay money arising out of a transaction in which the money, property, insurance or services which, are the subject of the transaction, are primarily for personal, family, or household purposes.”
Some examples of consumer debts are auto loans; medical expenses; charge cards, credit cards, mortgages, personal loans and so forth.
Many other laws pertain to commercial and business debts. To attempt to list them all is beyond the scope of this site. However, I suggest you start with the Uniformed Commercial Code and then look for state and federal laws concerning international and interstate commerce.