diff --git a/LightningCustodianWallet.test.js b/LightningCustodianWallet.test.js
index 82f6ab47..0903baee 100644
--- a/LightningCustodianWallet.test.js
+++ b/LightningCustodianWallet.test.js
@@ -247,4 +247,69 @@ describe('LightningCustodianWallet', () => {
     assert.equal(lOld.balance - oldBalance, 1);
     assert.equal(lNew.balance, 0);
   });
+
+  it('can pay free amount (tip) invoice', async function() {
+    jasmine.DEFAULT_TIMEOUT_INTERVAL = 100 * 1000;
+    if (!process.env.BLITZHUB) {
+      console.error('process.env.BLITZHUB not set, skipped');
+      return;
+    }
+
+    // fetchig invoice from tippin.me :
+
+    const api = new Frisbee({
+      baseURI: 'https://tippin.me',
+    });
+    const res = await api.post('/lndreq/newinvoice.php', {
+      headers: {
+        Origin: 'https://tippin.me',
+        'Accept-Encoding': 'gzip, deflate, br',
+        'Accept-Language': 'en-GB,en-US;q=0.9,en;q=0.8',
+        'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
+        Accept: 'application/json, text/javascript, */*; q=0.01',
+      },
+      body: 'userid=1188&username=overtorment&istaco=0&customAmnt=0&customMemo=',
+    });
+
+    let json;
+    let invoice;
+    if (res && res.body && (json = JSON.parse(res.body)) && json.message) {
+      invoice = json.message;
+    } else {
+      throw new Error('tippin.me problem: ' + JSON.stringify(res));
+    }
+
+    // --> use to pay specific invoice
+    // invoice =
+    //   'lnbc1pwrp35spp5z62nvj8yw6luq7ns4a8utpwn2qkkdwdt0ludwm54wjeazk2xv5wsdpu235hqurfdcsx7an9wf6x7undv4h8ggpgw35hqurfdchx6eff9p6nzvfc8q5scqzysxqyz5vqj8xq6wz6dezmunw6qxleuw67ensjnt3fldltrmmkvzurge0dczpn94fkwwh7hkh5wqrhsvfegtvhswn252hn6uw5kx99dyumz4v5n9sp337py2';
+
+    let l2 = new LightningCustodianWallet();
+    l2.setSecret(process.env.BLITZHUB);
+    await l2.authorize();
+    await l2.fetchTransactions();
+    await l2.fetchBalance();
+    let oldBalance = +l2.balance;
+    let txLen = l2.transactions_raw.length;
+
+    let decoded = await l2.decodeInvoice(invoice);
+    assert.ok(decoded.payment_hash);
+    assert.ok(decoded.description);
+    assert.equal(+decoded.num_satoshis, 0);
+
+    await l2.checkRouteInvoice(invoice);
+
+    let start = +new Date();
+    await l2.payInvoice(invoice, 3);
+    let end = +new Date();
+    if ((end - start) / 1000 > 9) {
+      console.warn('payInvoice took', (end - start) / 1000, 'sec');
+    }
+
+    await l2.fetchTransactions();
+    assert.equal(l2.transactions_raw.length, txLen + 1);
+    // transactions became more after paying an invoice
+
+    await l2.fetchBalance();
+    assert.equal(oldBalance - l2.balance, 3);
+  });
 });
diff --git a/class/lightning-custodian-wallet.js b/class/lightning-custodian-wallet.js
index 723deb05..9c0cacf7 100644
--- a/class/lightning-custodian-wallet.js
+++ b/class/lightning-custodian-wallet.js
@@ -102,9 +102,9 @@ export class LightningCustodianWallet extends LegacyWallet {
     this.secret = 'lndhub://' + json.login + ':' + json.password;
   }
 
-  async payInvoice(invoice) {
+  async payInvoice(invoice, freeAmount = 0) {
     let response = await this._api.post('/payinvoice', {
-      body: { invoice: invoice },
+      body: { invoice: invoice, amount: freeAmount },
       headers: {
         'Access-Control-Allow-Origin': '*',
         'Content-Type': 'application/json',
diff --git a/prompt.js b/prompt.js
index a09338f7..366962bb 100644
--- a/prompt.js
+++ b/prompt.js
@@ -1,6 +1,6 @@
 import prompt from 'react-native-prompt-android';
 
-module.exports = (title, text, isCancelable = true) => {
+module.exports = (title, text, isCancelable = true, type = 'secure-text') => {
   return new Promise((resolve, reject) => {
     const buttons = isCancelable
       ? [
@@ -30,7 +30,7 @@ module.exports = (title, text, isCancelable = true) => {
         ];
 
     prompt(title, text, buttons, {
-      type: 'secure-text',
+      type: type,
       cancelable: isCancelable,
     });
   });
diff --git a/screen/lnd/scanLndInvoice.js b/screen/lnd/scanLndInvoice.js
index ba29afb8..8bbd89d8 100644
--- a/screen/lnd/scanLndInvoice.js
+++ b/screen/lnd/scanLndInvoice.js
@@ -10,6 +10,7 @@ let BlueApp = require('../../BlueApp');
 let currency = require('../../currency');
 let EV = require('../../events');
 let loc = require('../../loc');
+let prompt = require('../../prompt');
 const { width } = Dimensions.get('window');
 
 export default class ScanLndInvoice extends React.Component {
@@ -92,6 +93,14 @@ export default class ScanLndInvoice extends React.Component {
     let decoded;
     try {
       decoded = await w.decodeInvoice(data);
+      let freeAmount = 0;
+      while (+decoded.num_satoshis === 0) {
+        freeAmount = await prompt('This is free amount invoice', 'How many satoshis do you want to tip?', false, 'numeric');
+        freeAmount = parseInt(freeAmount);
+        if (!isNaN(freeAmount) && freeAmount > 0) {
+          decoded.num_satoshis = freeAmount;
+        }
+      }
 
       let expiresIn = (decoded.timestamp * 1 + decoded.expiry * 1) * 1000; // ms
       if (+new Date() > expiresIn) {
@@ -105,6 +114,7 @@ export default class ScanLndInvoice extends React.Component {
         invoice: data,
         decoded,
         expiresIn,
+        freeAmount,
         destination: data,
       });
     } catch (Err) {
@@ -143,7 +153,7 @@ export default class ScanLndInvoice extends React.Component {
         let start = +new Date();
         let end;
         try {
-          await fromWallet.payInvoice(this.state.invoice);
+          await fromWallet.payInvoice(this.state.invoice, this.state.freeAmount);
           end = +new Date();
         } catch (Err) {
           console.log(Err.message);
@@ -170,7 +180,24 @@ export default class ScanLndInvoice extends React.Component {
 
   render() {
     return (
-      <TouchableWithoutFeedback onPress={Keyboard.dismiss} accessible={false}>
+      <TouchableWithoutFeedback
+        onPress={async () => {
+          if (this.state.freeAmount) {
+            // must ask user again about the amount
+            let freeAmount = await prompt('This is free amount invoice', 'How many satoshis do you want to tip?', false, 'numeric');
+            freeAmount = parseInt(freeAmount);
+            if (!isNaN(freeAmount) && freeAmount > 0) {
+              let decoded = this.state.decoded;
+              decoded.num_satoshis = freeAmount;
+              this.setState({ decoded, freeAmount });
+              Keyboard.dismiss();
+            }
+          } else {
+            Keyboard.dismiss();
+          }
+        }}
+        accessible={false}
+      >
         <SafeBlueArea forceInset={{ horizontal: 'always' }} style={{ flex: 1 }}>
           <Text style={{ textAlign: 'center', fontSize: 50, fontWeight: '700', color: '#2f5fb3' }}>
             {this.state.hasOwnProperty('decoded') &&