Maybe encryption it’s too much or too hard.
But some checksum with key will be good
Checksum(payload+key)
Or base64+checksum
Syncword it’s not enough, anyone can fake data
Working
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Very cute 
Send on /LORAtoMQTT/1000_EB3 msg {“id”:“1000_EB3”,“Ser”:1,“ERR”:80,“up”:15178,“Clock”:“21:49:38”,“VL1”:2386,“CL1”:5,“VL2”:2380,“CL2”:0,“VL3”:2372,“CL3”:10,“CLT”:15,“FR”:500,“PF”:968,“PF1”:874,“PF2”:853,“PF3”:993,“API”:306,“APE”:0,“API1”:108,“APE1”:0,“API2”:7,“APE2”:0,“API3”:190,“APE3”:0,“TET1”:5897107,“TET2”:3339484,“TET3”:7694978,“TEI”:16931579,“TEE”:564,“rssi”:-80,“snr”:9.5,“pferror”:-528,“packetSize”:128}