The invoice should have like 8 lines, each line presents an item with its description and price.
I used a math field for the price.
Whenever a math field is note used (left empty), it shows a value "0" when I print the report. While it should only appear as blank line.
I set the field to invisible by rule only when edit (value entered), but still appearing "0"
(suena raro, porque habla español, cambiate el nombre jajja)
i think that you should try to edit the math format, (where you set the number of decimals and so...) if you are using a spanish version, please, note that fore some reason, the traduction messed up the format, so even if using the asistants you get a format like this "matematicas ##.00, you have to manually change it to english, "math ##.00
play with the options untill you get what you need, but almost for shure, you have a format issue.