SDR branches selector

Hello community

I am using Gnuradio 3.7.

I want to select one of two implemented modulators to be sent to an SDR device. (i.e., branch_1 & branch_2) 

They both have the same sampling rate.

When I send ( branch_1 * 0 + branch_2 ), the demodulator of the receiving side doesn't decode the messages.

When I send ( branch_2 ), the demodulator of the receiving side decodes the messages correctly.

When I send (branch_2 * 0 + branch_2), the demodulator of the receiving side decodes the messages correctly.

I couldn't figure out what is the problem.

Please help me to make this design work!

and tell me if there is a better way to implement the modulation selector with the available blocks?

With best regards

Yasir