RF433 Transmitter with Pro Mini

I have set up a WeMos D1 R1 with a RF 433 receiver and an Arduino Uno with the corresponding transmitter. This all works fine and I am getting the expected outputs on the console.

I would like the transmitter to run from a Pro Mini (possibly chinese copy). I need more practice with soldering some some of the header pins are a bit dodgy but I have identified 3 that will happily light an LED. I was therefore planning on using these 3 pins for VCC, GND and Data. I have wired it all up and uploaded the same sketch as on the Uno (albeit modified to define the VCC and GND pins) but nothing is appearing on my WeMos console. To check that the pins were working I have also tried using a DHT11 and this seemed to work fine. It therefore looks to be something to do with the Pro Mini rather than anything else. Could it be that the transmitter isn't getting enough power?

Any other things I should be checking?

(Also, this is my first post in this forum so apologies if I have put this in the wrong place).

Thanks