Add cypress tests

packages/extension/cypress/e2e/payments.cy.ts

@@ -399,4 +399,39 @@ describe('Make payment from the UI', () => {
     });
     cy.get('p[data-testid="transaction-subtitle"]').should('have.text', 'Transaction Successful');
   });
+
+  it('Should correctly pay with custom fees', () => {
+    navigate(HOME_URL, PASSWORD);
+
+    cy.contains('button', 'Send').click();
+
+    // Input recipient's address
+    cy.get('#recipient-address').type(DESTINATION_ADDRESS);
+
+    // Input amount
+    cy.get('#amount').clear().type('0.01').should('not.have.class', 'Mui-error');
+
+    // Input new fees (optional)
+    cy.get('#transaction-fee').clear().type('0.000025').should('not.have.class', 'Mui-error');
+
+    // Click on the Send Payment button
+    cy.get('button').contains('Send Payment').click();
+
+    // Check that the fees are correct
+    cy.contains('Network fees:').next().should('have.text', '0.000025 XRP');
+
+    // Confirm the payment
+    cy.contains('button', 'Confirm').click();
+
+    cy.get('h1[data-testid="transaction-title"]').should('have.text', 'Transaction in progress');
+    cy.get('p[data-testid="transaction-subtitle"]').should(
+      'have.text',
+      'We are processing your transactionPlease wait'
+    );
+
+    cy.get('h1[data-testid="transaction-title"]').contains('Transaction accepted', {
+      timeout: 10000
+    });
+    cy.get('p[data-testid="transaction-subtitle"]').should('have.text', 'Transaction Successful');
+  });
 });