A declined transaction does not deduct the transaction amount itself from your account — you can confirm this by checking your balance/transaction history in the app.
⚠️ Note on the Declined Fee: If the decline is due to something on your end (e.g. insufficient balance, a frozen/reported-lost card, or incorrect card details), the first 5 declined transactions per account each month are fee-free — from the 6th one onward, a $0.80 USD Declined Fee applies per transaction. See MPChat Card Limits and Fees and the validation and declined-transaction fee guide.