SSTV with FT-757GX2 and MMSSTV

Good evening everyone,
for FT4/FT8 I use the FT-757GX2, WJST-X, Digirig and the Yaesu GX16 Mic Cable. That works very well. But if I want to make SSTV with MMSSTV 1.13.3 I can only receive. No matter what setting I make, no signal comes out. Without Omni-Rig I can switch on TX, but there are no sounds. If I switch on the Omni-Rig and set the FT-757GXII, the transmitter turns on immediately. I’ve been researching for a few hours but can’t find the error. Does anyone here have a tip for me? 73 de DD8BV, Norbert