Screen or indicator fails to light up (1:02 to 2:25)

Try to use the new batteries. We would recommend using some famous alkaline batteries like Duracell or high-end rechargeable batteries.
2If there are still no lights when pressing the “Power” button, connect the power plug to another power source.

Not synced (2:25 to 3:34)

Ensure there is enough power. You can replace the batteries with fresh ones for the transmitter to avoid power-related issues.
Change the frequency for mic B and mic C. Click the set button on the top of the transmitter for one MHz increments. Try as many different channels as possible to check if both indicators stay on. If not? Reset it.

Make sure all units are off, including other wireless microphones you are using.
Turn on the transmitter B and click the set button on top 10 times in a row within 30 seconds to enter the reset mode. The 605 MHz flashes if you do it right. The same procedure goes for transmitters C, but 584 MHz will flash if you do it right. If no special channel is flashing, just go back to step 1 to do the procedure again.
When the screens are flashing, power the receiver on; meanwhile, the RF.B and RF.C indicators turn green, flash three times, and extinguish.
One click SET button to confirm one by one.
If the transmitter stops flashing, the frequency has changed to another available frequency, and the indicators turn solid green, pairing is successful.

605/584 MHz are special frequencies that will only appear in the reset mode, not included in the regular frequency channels.

Check if the connection is correct. Instead of an aux line, we suggest using the quarter-inch mic input on a speaker/amplifier/mixer. Also, smartphones, iPads, or computers are for streaming background music to the K038, not for recording.
Replace the batteries with fresh ones for the transmitter to avoid virtual power.
Check if the receiver works properly. Turn off the transmitters to see if the RF.B and RF.C indicators go off. Then turn it back on to check if the indicators are on. If both are yes, the receiver is fine.
Bluetooth speakers could accept single input signals, disconnect Bluetooth, or be used with another speaker.
Check if the K038 goes wrong: If you have other microphones with a quarter-inch output connector, test them with the speaker. If you have another speaker with a quarter-inch mic input, then test the speaker with the K038.
Make sure you're wearing the mic correctly.