"I sent exactly the invoice amount, so why does it say I underpaid?" is one of the most common confusions in crypto payments. The cause is usually not on the merchant's side but on the sending side.
Bitrefill's help centre puts it plainly: an invoice reads underpaid order when the total amount due was not fully paid, and the common cause is that "if you used a centralized exchange, custodial wallet, or other third-party platform, like a bridge, these services usually deduct fees from the amount sent." You typed 100; what arrived was 99-something.
This guide covers the cause and the fix. It quotes no fee figures — how much is deducted is set by whichever platform you sent from.
Key points
- The shortfall is usually a fee taken by the sending platform, not a merchant error
- You can normally either top up the difference or ask for the paid amount back
- Top-up payments must use the address and amount on the current invoice
- A self-custody wallet or a pre-funded balance avoids the problem entirely
- Check the invoice is still valid before sending anything more
Why the amount falls short
The merchant's invoice specifies what must arrive. Many sending interfaces, though, treat the number you type as what leaves your account, with the fee taken out of it. The gap between those two figures is exactly what the invoice is missing.
Bitrefill's explanation points at third-party platforms: centralised exchanges, custodial wallets and bridges usually deduct their fee from the amount sent. Self-custody wallets typically charge the network fee separately rather than out of the transfer, so the problem is rarer there.
| How you sent it | What the number you type usually means | Prone to underpaying |
|---|---|---|
| Centralised exchange withdrawal | Total deducted from your account | Yes — the fee often comes out of it |
| Custodial wallet or bridge | Varies, often the total deducted | Yes |
| Self-custody wallet | The transfer amount, fee charged separately | Less often |
| Pre-funded platform balance | Deducted from the balance | No network fee involved |
What you can do once it happens
Bitrefill's article gives two paths: send the remaining balance to complete the invoice, or, if you would rather not finish paying, request a refund of what you already sent, following the instructions on the invoice.
Which one fits depends on whether you still want the order and whether the invoice is still live. If it has expired, a top-up payment may no longer be credited to the original order, so confirm the status first.
- Still want it: while the invoice is valid, send the shortfall to the address it currently shows.
- No longer want it: follow the refund instructions on the invoice for what you already sent.
- Not sure: contact official support with the invoice ID and transaction hash before sending anything more.
The second payment is where people slip again
Topping up is a second transfer, so every check has to be repeated — and it is easier to skip them, because it feels like you just did all this.
- Use the address the invoice shows now; do not copy it from the previous transfer.
- Use the network the invoice requires; do not switch to a cheaper one.
- Send the shortfall the invoice states, not the original amount.
- If you are sending from an exchange again, it will deduct a fee again — add it on, or send a different way.
Avoiding it next time
Bitrefill's article suggests two preventions: use a non-custodial wallet, where you hold the private keys, or pre-fund your balance on the platform so individual payments are not exposed to third-party deductions.
If an exchange is your only option, read the withdrawal screen carefully to see whether the figure is what you pay or what they receive. Most exchanges show the amount that will arrive, so work backwards from what the invoice requires.
Frequently asked questions
What if I overpaid instead?
Bitrefill's help centre covers this separately: once the funds are received you can start a refund directly from the invoice, choosing either your platform balance or a wallet address. Other platforms set their own rules.
Will the order continue automatically after I top up?
Usually, if the invoice is still valid and the total is now met. If it has expired, the additional funds may have to go through a refund rather than completing the order, so check the status before sending.
Is this only a Bitrefill thing?
No. Any crypto invoice requiring an exact amount hits the same mechanism, because the shortfall is created on the sending side, not the receiving side. Each platform handles it differently.
Can the merchant just accept what arrived?
That depends on their system; most match the invoice amount exactly. Rather than relying on manual handling, add the fee in when you send.
Sources
Public sources used for this guide. Sources checked on 2026-09-09. We have not tested this with a real purchase.
- Bitrefill help centre: why does my invoice say underpaid orderReviewed 2026-09-09
- Bitrefill help centre: I accidentally overpaid or sent too much cryptoReviewed 2026-09-09