What is the relationship between PLAYERS and sponsorship_PLAYERS? You are going to a layout based on the first and then specifying search criteria in the second. From the naming convention used, these are two Tutorial: What are Table Occurrences?, but the relationship, if any, between the two will affect your results. I suspect that either your go to layout step should go to a layout based on sponsorship_PLAYERS or your set field should refer to PLAYERS.
Then to specify that Invoice # be empty, you use set field to put "=" as the criteria in that field.
Worked perfectly - thank you PhilModJunk..