Failure to deliver MMS/SMS from iPhone on Cricket

Two phone calls to Cricket support and one visit to a Cricket office have failed to remedy this problem. While I seem to receive MMS (pictures) fine more often than not I can not send. And lately have started having troubles with simple plain short text messages. Sometimes "retry" succeeds.

Online search for others with same issue on iOS has not been successful. Not even here, so I'm asking. Others say on Android that DNS gives an unreachable address from WiFi and the public internet, that one needs the IP address of server which is only reachable on Cricket's (AT&T?) private cell network. That doesn't appear to be a settable parameter in iOS, and until recently disabling WiFi + reboot seems to solve the problem. But now with WiFi off the problem is returning.

Attempt to send text and picture in the same message is almost guaranteed failure. Or two pictures. Thin green bar appears near the top in Messages and stops about 95% across the screen. For minutes. Then the failure message appears.

An interesting observation is how with WiFi disabled on iPhone an MMS message sent from iPad which must relay through iPhone does not appear on the iPhone until the iPad indicates the message has been sent. But when WiFi is enabled on the iPhone the iPad message appears on iPhone (and Mac) almost instantly. And then some minutes later all devices get the failure message. But if WiFi disabled on iPhone only the iPhone gets failure message.

Of course everything works perfectly if the recipient is on iCloud.