In case you are not able to enter all the information from your 1042-S in Sprintax you might not be able to prepare your US tax return with us.
Not all boxes are mandatory to be filled even if you have them on your 1042-S form (or any other income document), however, just to be sure how to proceed, it is best to contact our Customer Support team or send us an email with your exact query, your registration email address and a screenshot of the box you are unable to fill here - info@sprintax.com