Go back to basics. Your first screen shot shows a receipt from a Payer. Receipts debit the bank or cash account to which they are assigned and credit the account(s) selected for the line items. Because you made the agent’s commission negative, what would normally be a credit turns into a debit. A debit reduces a credit account, like your Agents’ Commision liability account. So after the first screen shot, the balance would be -10.
Your second screen shot shows a payment, which credits the bank or cash account and debits the line item account, again driving it more negative. After the second screen shot, the balance is -20, exactly as it should be.
The question is why you entered the commission as a negative number in the first place. You wanted to credit a liability account, so it should have been a positive number. How much did the customer actually pay? If they paid you 90, you should have split the receipt into two line items, 80 going to Application forms sold as income and 10 to Agents’ Commission as the liability. If they paid you 100, you should have split the receipt 90 and 10.
As an aside, some will say the commission should not be recorded as a liability to begin with. Especially if the sale was taxable, the full amount of the sale should go to an income account. Then, the commission could be entered as an expense to offset it, posting to an expense account. What you have done (even when corrected as described above) understates gross income. Depending on your tax law, that could be illegal.