I know that when we sell some goods abroad, we credit Goods&Services part within Trade balance, which is a part of Current Account.
What part of the Financial Account is debited with the sum received for the exported goods?
The physical part of trade in goods and services is recorded in the Current Account and the payment (with financial assets) part of the transaction is recorded in the Financial Account. The Balance of Payments should be 0 after you sum up the Current Account balance, the Capital Account and the Financial Account balances. The trade in goods and services is recorded in Current Accounts. For instance, exports are credited and imports are debited.
It is recorded under the "Other investment" of the Financial Account.
The BPM6, Chapter 6 divides the Financial Account into five portions:
"Other investment" (p. 111, BPM6) sounds unimportant , but is actually where payments for exports and imports are (usually) recorded, because this category includes: currency and deposits; loans; and trade credit and advances.
Example. A US farm exports \$100 worth of beef to a Japanese supermarket. The Japanese supermarket pays \$100 and this is deposited into the US farm's bank account.
From the American perspective, the export is recorded as a credit (+) under Current Account: Exports. And the payment is recorded as a debit (-) under Financial Account: Other investments.
Conversely, from the Japanese perspective, the import is recorded as a debit (-) under Current Account: Exports. And the payment is recorded as a credit (+) under Financial Account: Other investments.
The question refers to the double-entry bookkeeping principle used in balance of payments accounting. Each transaction must appear twice in the balance of payments, once as debit and once as a credit.
An imported good can be paid for by (1) transferring money from a bankaccount in the importing country to a bank account in the exporting country, (2) cash can be transferred or (3) the importing country may be incurring a liability (the obligation to pay for the goods), while the exporting country acquires an asset (the receiving of a future payment).
These transactions are, without any doubt, registered somewhere in the financial account. I am not entirely sure, but I believe all three situations would be registered as portfolio investments.
The sixth IMF BoP manual says the following:
For example, the corresponding entry for an export of goods is usually an increase in financial assets, such as currency and deposits or trade credit.
I'm not also quite sure about what you're asking here. When we sell some goods abroad, we credit Goods&Services part within Trade balance with the sum received for the exported goods. We credit the values of trade in dollars, not the quantities. There is not necessarily a counterpart in the Financial Account. For instance, a trade relationship within the eurozone is priced in euros and does not affect the partner's financial account.
As explained in the Chapter 13 of the Krugman, Obstfeld, Melitz, International Economics.
Transactions that arise from the export or import of goods or services and therefore enter directly into the current account. When a French consumer imports American blue jeans, for example, the transaction enters the U.S. balance of payments accounts as a credit on the current account.
Note that in this example, as pointed out by @denesp, a euro/dollar trade could be needed. This will affect the financial account as well. However, trade is operated by large (multinational) firms, which have bank accounts in the major currencies such as USD and euro.