Change the control Source in a textbox in a Report. (1 Viewer)

Change the Control Source of a TextBox in a report. Like the one shown in this image:


Screen capture

My aim is to exclude from this control results that are compabtile with the string above depicted so I've written:


But it does not work. So my question to all the community is clear: How to prevent some strings that show the kind of FormaPago (there are several) to be printed in the report.

Why the way I've used is not correct? How to solve this?

=IIf([FormaPago] = "Transferencias SVS-Mutuas", Null, [FormaPago])

Or apply filter criteria to report so those records are not retrieved.

use Conditional Formatting.

@arnelgp, could you clarify how CF applies?