Please run DMR AutoCal, or manually adjust the RX offset on the Modem page in +-100Hz steps from -500Hz to +500Hz for the lowest BER. You can verify settings using the openSPOT's built-in local echo service on DMR ID 9999.
If AutoCal does not work for you then the RX offset between the transceiver and the openSPOT is greater than 500Hz. What you can do is to switch frequencies on the openSPOT, but keep the transceiver's frequency. For example, if the transceiver is on 433.900MHz, then test by setting the openSPOT to the following frequencies:
You can use the built-in local echo service to test your own voice on DMR ID 9999.