Hello Andrea,
I'm not sure want you mean by "send de amout discount".
Just to clarify, in Jasmin you have 2 ways of setting a discount:
1 - In percentage
At the document's general data and at each document line (where you can set up to 3 incremental discounts - this ones will be applied cumulatively to the discount seted at the document's general data).
2- In value
At the document's general data in the "Financial" Expander, in attribute "Discount in Value"
This will also be applied in a cumulative way to the discounts defined at 1 (in percentage) but there is no way for you to set the discount in value for each document line (you cannot do by WebAPI an operation not supported by the application).
Regarding this case, be sure you know want you are doing when using this attribute. The way the value is used in calculations, depends on either or not your document prices are "Tax Inclusive" (be sure to make some tests in the application interface in order to validate what you are trying to achive).
If you do want do use the "discountinvalue" attribute, it is included at the WebApi documentation
https://jasminsoftware.github.io/billing.invoices.html#ApiInvoiceResource
Attribute "discountInValueAmount" (keep in mid that this attribute is a MoneyResource)
