import ch.codeblock.qrinvoice.model.QrInvoice;
import ch.codeblock.qrinvoice.model.builder.QrInvoiceBuilder;
import ch.codeblock.qrinvoice.model.validation.ValidationException;
import ch.codeblock.qrinvoice.model.validation.ValidationResult;

// ...
try {
    final QrInvoice qrInvoice = QrInvoiceBuilder
    .create()
    .creditorIBAN("CH44 3199 9123 0008 8901 2")
    .paymentAmountInformation(p -> p
// Important part is here: The amount can be left out, however currency must be set
        .chf()
    )
    .creditor(c -> c
        .structuredAddress()
        .name("Robert Schneider AG")
        .streetName("Rue du Lac")
        .houseNumber("1268")
        .postalCode("2501")
        .city("Biel")
        .country("CH")
    )
    .ultimateDebtor(d -> d
        .structuredAddress()
        .name("Pia-Maria Rutschmann-Schnyder")
        .streetName("Grosse Marktgasse")
        .houseNumber("28")
        .postalCode("9400")
        .city("Rorschach")
        .country("CH")
    )
    .paymentReference(r -> r
        .qrReference("210000000003139471430009017")
    )
    .additionalInformation(a -> a
        .unstructuredMessage("Instruction of 03.04.2019")
        .billInformation("//S1/10/10201409/11/190512/20/1400.000-53/30/106017086/31/180508/32/7.7/40/2:10;0:30")
    )
    .alternativeSchemeParameters(Arrays.asList(
        "Name AV1: UV;UltraPay005;12345",
        "Name AV2: XY;XYService;54321"
    ))
    .build();
} catch (ValidationException validationException) {
    final ValidationResult validationResult = validationException.getValidationResult();
    // handle exception...
}