If It’s less than 48 hours since you bought an app, you can request a refund through Google Play.
A refund is not possible 48 hours after purchasing an app, due to company policy.

Encodes audio coming in through the internal microphone input to DRM30 (Digital Radio Mondiale) signals.
(Send generated DRM signal to smartphone speaker output.)

The DRM+ Tx app is for DRM30 encoding with OPUS. The paid DRM+ Tx app encodes sound, text label and message.

The DRM+ Tx app requires a RC high pass filter audio line as well as a RF front-end module with antenna, tuner, modulator, IF mixer, AF amplifier.

If a call is received while the app is running, please remove the audio line connected to the headphone jack.