My wife and I are both on Lum. She can send me texts but has not been receiving texts from me for 2 days now. Sending and receiving texts works for both of us for every other person we have talked to.
What type of device are you on? Sometimes the trouble could be with iMessage on iPhone or RCS on android. So double check those if you can and also toggle airplane mode a few times to see if that resolves any issues.
If you continue to have problems, raise a ticket in your lum account.